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SubjectRe: Deadlock on the mm->mmap_sem
Andrea Arcangeli wrote:
> > elf_core_dump should call down_write to prevent concurrent expand_stack
>
> expand_stack doesn't need the write sem, see the locking comments in the
> 00_silent-stack-overflow patch in -aa.
>
You misunderstood me, it's the other way around:
elf_core_dump walks the vma list twice and assumes that the segment
sizes don't change --> elf_core_dump needs a write lock to ensure that.

> > calls, and acquire the pagetable_lock around some lines (right now it
> > walks the page tables without locking). I'll check the other coredump
>
> Also expand_stack needs the page_table_lock, that's ok.
>
Dito: elf_core_dump walks the page tables without locking.

> > I'll write a patch that moves the locking into the coredump handlers,
> > then we can compare that with Andrea's proposal.
>
> Ok.
>
Attached is a beta version:

* remove {down,up}_read from fs/exec.c::do_coredump
* add down_read into each arch/*/process.c::dump_thread. Most of them
are probably save without the locking, but it's better for the
consistency. Most of them access mm->brk and perform some calculations.
* explicit memset(,0,) around all structures that are dumped in
fs/binfmt_elf.c: depending on the structure alignment, we could
otherwise leak kernel stack.
* Do not walk the vma list twice, copy it into a temporary kernel
buffer. down_write around it to prevent concurrent expand_stack.
* spin_lock(&current->mm->page_table_lock) around the code that walks
the page tables.
* all other binfmt's have trivial coredump implementation that only call
dump_thread, or no coredump at all.

I'll do more extensive testing tomorrow.

--
Manfred// $Header$
// Kernel Version:
// VERSION = 2
// PATCHLEVEL = 4
// SUBLEVEL = 10
// EXTRAVERSION =-pre12
diff -ur 2.4/fs/binfmt_elf.c build-2.4/fs/binfmt_elf.c
--- 2.4/fs/binfmt_elf.c Wed Sep 19 22:39:35 2001
+++ build-2.4/fs/binfmt_elf.c Thu Sep 20 22:48:52 2001
@@ -31,6 +31,7 @@
#include <linux/init.h>
#include <linux/highuid.h>
#include <linux/smp_lock.h>
+#include <linux/vmalloc.h>

#include <asm/uaccess.h>
#include <asm/param.h>
@@ -895,22 +896,22 @@
*
* I think we should skip something. But I am not sure how. H.J.
*/
-static inline int maydump(struct vm_area_struct *vma)
+static inline int maydump(unsigned long flags)
{
/*
* If we may not read the contents, don't allow us to dump
* them either. "dump_write()" can't handle it anyway.
*/
- if (!(vma->vm_flags & VM_READ))
+ if (!(flags & VM_READ))
return 0;

/* Do not dump I/O mapped devices! -DaveM */
- if (vma->vm_flags & VM_IO)
+ if (flags & VM_IO)
return 0;
#if 1
- if (vma->vm_flags & (VM_WRITE|VM_GROWSUP|VM_GROWSDOWN))
+ if (flags & (VM_WRITE|VM_GROWSUP|VM_GROWSDOWN))
return 1;
- if (vma->vm_flags & (VM_READ|VM_EXEC|VM_EXECUTABLE|VM_SHARED))
+ if (flags & (VM_READ|VM_EXEC|VM_EXECUTABLE|VM_SHARED))
return 0;
#endif
return 1;
@@ -967,6 +968,7 @@
{
struct elf_note en;

+ memset(&en,0,sizeof(en));
en.n_namesz = strlen(men->name);
en.n_descsz = men->datasz;
en.n_type = men->type;
@@ -989,6 +991,46 @@
#define DUMP_SEEK(off) \
if (!dump_seek(file, (off))) \
goto end_coredump;
+
+struct elf_dumpinfo {
+ unsigned long start;
+ size_t len;
+ unsigned long flags;
+};
+
+static struct elf_dumpinfo * alloc_dumpinfo(int segs)
+{
+ int len = sizeof(struct elf_dumpinfo)*segs;
+ if (len < PAGE_SIZE)
+ return kmalloc(len, GFP_KERNEL);
+ return vmalloc(len);
+}
+
+void free_dumpinfo(struct elf_dumpinfo * ptr, int segs)
+{
+ int len = sizeof(struct elf_dumpinfo)*segs;
+ if (len < PAGE_SIZE)
+ return kfree(ptr);
+ return vfree(ptr);
+}
+
+static struct elf_dumpinfo *get_dumpinfo(void)
+{
+ int i;
+ struct vm_area_struct *vma;
+ struct elf_dumpinfo *di = alloc_dumpinfo(current->mm->map_count);
+ if (!di)
+ return NULL;
+
+ vma = current->mm->mmap;
+ for(i = 0, vma = current->mm->mmap; vma != NULL; i++,vma = vma->vm_next) {
+ di[i].start = vma->vm_start;
+ di[i].len = vma->vm_end - vma->vm_start;
+ di[i].flags = vma->vm_flags;
+ }
+ if (i != current->mm->map_count) BUG();
+ return di;
+}
/*
* Actual dumper
*
@@ -1003,7 +1045,6 @@
int segs;
size_t size = 0;
int i;
- struct vm_area_struct *vma;
struct elfhdr elf;
off_t offset = 0, dataoff;
unsigned long limit = current->rlim[RLIMIT_CORE].rlim_cur;
@@ -1012,19 +1053,26 @@
struct elf_prstatus prstatus; /* NT_PRSTATUS */
elf_fpregset_t fpu; /* NT_PRFPREG */
struct elf_prpsinfo psinfo; /* NT_PRPSINFO */
+ struct elf_dumpinfo *di;

+ /* stop all vm operations, including expand_stack */
+ down_write(&current->mm->mmap_sem);
segs = current->mm->map_count;
+ di = get_dumpinfo();
+ up_write(&current->mm->mmap_sem);
+ if (!di)
+ return 0;

#ifdef DEBUG
printk("elf_core_dump: %d segs %lu limit\n", segs, limit);
#endif

/* Set up header */
+ memset(&elf, 0, sizeof(elf));
memcpy(elf.e_ident, ELFMAG, SELFMAG);
elf.e_ident[EI_CLASS] = ELF_CLASS;
elf.e_ident[EI_DATA] = ELF_DATA;
elf.e_ident[EI_VERSION] = EV_CURRENT;
- memset(elf.e_ident+EI_PAD, 0, EI_NIDENT-EI_PAD);

elf.e_type = ET_CORE;
elf.e_machine = ELF_ARCH;
@@ -1156,42 +1204,34 @@
for(i = 0; i < numnote; i++)
sz += notesize(&notes[i]);

+ memset(&phdr, 0, sizeof(phdr));
phdr.p_type = PT_NOTE;
phdr.p_offset = offset;
- phdr.p_vaddr = 0;
- phdr.p_paddr = 0;
phdr.p_filesz = sz;
- phdr.p_memsz = 0;
- phdr.p_flags = 0;
- phdr.p_align = 0;

offset += phdr.p_filesz;
DUMP_WRITE(&phdr, sizeof(phdr));
- }

- /* Page-align dumped data */
- dataoff = offset = roundup(offset, ELF_EXEC_PAGESIZE);
+ /* Page-align dumped data */
+ dataoff = offset = roundup(offset, ELF_EXEC_PAGESIZE);

- /* Write program headers for segments dump */
- for(vma = current->mm->mmap; vma != NULL; vma = vma->vm_next) {
- struct elf_phdr phdr;
- size_t sz;
+ /* Write program headers for segments dump */
+ for(i = 0;i < segs; i++) {

- sz = vma->vm_end - vma->vm_start;
+ phdr.p_type = PT_LOAD;
+ phdr.p_offset = offset;
+ phdr.p_vaddr = di[i].start;
+ phdr.p_paddr = 0;
+ phdr.p_filesz = maydump(di[i].flags) ? di[i].len : 0;
+ phdr.p_memsz = di[i].len;
+ offset += phdr.p_filesz;
+ phdr.p_flags = di[i].flags & VM_READ ? PF_R : 0;
+ if (di[i].flags & VM_WRITE) phdr.p_flags |= PF_W;
+ if (di[i].flags & VM_EXEC) phdr.p_flags |= PF_X;
+ phdr.p_align = ELF_EXEC_PAGESIZE;

- phdr.p_type = PT_LOAD;
- phdr.p_offset = offset;
- phdr.p_vaddr = vma->vm_start;
- phdr.p_paddr = 0;
- phdr.p_filesz = maydump(vma) ? sz : 0;
- phdr.p_memsz = sz;
- offset += phdr.p_filesz;
- phdr.p_flags = vma->vm_flags & VM_READ ? PF_R : 0;
- if (vma->vm_flags & VM_WRITE) phdr.p_flags |= PF_W;
- if (vma->vm_flags & VM_EXEC) phdr.p_flags |= PF_X;
- phdr.p_align = ELF_EXEC_PAGESIZE;
-
- DUMP_WRITE(&phdr, sizeof(phdr));
+ DUMP_WRITE(&phdr, sizeof(phdr));
+ }
}

for(i = 0; i < numnote; i++)
@@ -1202,29 +1242,29 @@

DUMP_SEEK(dataoff);

- for(vma = current->mm->mmap; vma != NULL; vma = vma->vm_next) {
+ for(i = 0;i < segs; i++) {
unsigned long addr;

- if (!maydump(vma))
+ if (!maydump(di[i].flags))
continue;
#ifdef DEBUG
printk("elf_core_dump: writing %08lx %lx\n", addr, len);
#endif
- for (addr = vma->vm_start;
- addr < vma->vm_end;
- addr += PAGE_SIZE) {
+ for (addr = di[i].start; addr < di[i].start+di[i].len; addr += PAGE_SIZE) {
pgd_t *pgd;
pmd_t *pmd;
- pte_t *pte;
-
- pgd = pgd_offset(vma->vm_mm, addr);
+ pte_t pte;
+
+ spin_lock(&current->mm->page_table_lock);
+ pgd = pgd_offset(current->mm, addr);
if (pgd_none(*pgd))
goto nextpage_coredump;
pmd = pmd_offset(pgd, addr);
if (pmd_none(*pmd))
goto nextpage_coredump;
- pte = pte_offset(pmd, addr);
- if (pte_none(*pte)) {
+ pte = *pte_offset(pmd, addr);
+ spin_unlock(&current->mm->page_table_lock);
+ if (pte_none(pte)) {
nextpage_coredump:
DUMP_SEEK (file->f_pos + PAGE_SIZE);
} else {
@@ -1241,6 +1281,7 @@

end_coredump:
set_fs(fs);
+ free_dumpinfo(di, segs);
return has_dumped;
}
#endif /* USE_ELF_CORE_DUMP */
diff -ur 2.4/fs/exec.c build-2.4/fs/exec.c
--- 2.4/fs/exec.c Wed Sep 19 22:39:35 2001
+++ build-2.4/fs/exec.c Thu Sep 20 19:41:24 2001
@@ -969,9 +969,7 @@
if (do_truncate(file->f_dentry, 0) != 0)
goto close_fail;

- down_read(&current->mm->mmap_sem);
retval = binfmt->core_dump(signr, regs, file);
- up_read(&current->mm->mmap_sem);

close_fail:
filp_close(file, NULL);
diff -ur 2.4/arch/alpha/kernel/process.c build-2.4/arch/alpha/kernel/process.c
--- 2.4/arch/alpha/kernel/process.c Wed Sep 19 22:39:31 2001
+++ build-2.4/arch/alpha/kernel/process.c Thu Sep 20 21:26:54 2001
@@ -344,6 +344,7 @@
struct switch_stack * sw = ((struct switch_stack *) pt) - 1;

dump->magic = CMAGIC;
+ down_read(&current->mm->mmap_sem);
dump->start_code = current->mm->start_code;
dump->start_data = current->mm->start_data;
dump->start_stack = rdusp() & ~(PAGE_SIZE - 1);
@@ -353,6 +354,7 @@
>> PAGE_SHIFT);
dump->u_ssize = (current->mm->start_stack - dump->start_stack
+ PAGE_SIZE-1) >> PAGE_SHIFT;
+ up_read(&current->mm->mmap_sem);

/*
* We store the registers in an order/format that is
diff -ur 2.4/arch/arm/kernel/process.c build-2.4/arch/arm/kernel/process.c
--- 2.4/arch/arm/kernel/process.c Wed Sep 19 22:39:31 2001
+++ build-2.4/arch/arm/kernel/process.c Thu Sep 20 21:27:45 2001
@@ -339,11 +339,13 @@
struct task_struct *tsk = current;

dump->magic = CMAGIC;
+ down_read(&tsk->mm->mmap_sem);
dump->start_code = tsk->mm->start_code;
dump->start_stack = regs->ARM_sp & ~(PAGE_SIZE - 1);

dump->u_tsize = (tsk->mm->end_code - tsk->mm->start_code) >> PAGE_SHIFT;
dump->u_dsize = (tsk->mm->brk - tsk->mm->start_data + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ up_read(&tsk->mm->mmap_sem);
dump->u_ssize = 0;

dump->u_debugreg[0] = tsk->thread.debug.bp[0].address;
diff -ur 2.4/arch/cris/kernel/process.c build-2.4/arch/cris/kernel/process.c
--- 2.4/arch/cris/kernel/process.c Wed Sep 19 22:39:31 2001
+++ build-2.4/arch/cris/kernel/process.c Thu Sep 20 21:28:38 2001
@@ -227,8 +227,10 @@
dump->magic = CMAGIC;
dump->start_code = 0;
dump->start_stack = regs->esp & ~(PAGE_SIZE - 1);
+ down_read(&current->mm->mmap_sem);
dump->u_tsize = ((unsigned long) current->mm->end_code) >> PAGE_SHIFT;
dump->u_dsize = ((unsigned long) (current->mm->brk + (PAGE_SIZE-1))) >> PAGE_SHIFT;
+ up_read(&current->mm->mmap_sem);
dump->u_dsize -= dump->u_tsize;
dump->u_ssize = 0;
for (i = 0; i < 8; i++)
diff -ur 2.4/arch/i386/kernel/process.c build-2.4/arch/i386/kernel/process.c
--- 2.4/arch/i386/kernel/process.c Wed Sep 19 22:39:31 2001
+++ build-2.4/arch/i386/kernel/process.c Thu Sep 20 19:47:58 2001
@@ -611,8 +611,10 @@
dump->magic = CMAGIC;
dump->start_code = 0;
dump->start_stack = regs->esp & ~(PAGE_SIZE - 1);
+ down_read(&current->mm->mmap_sem);
dump->u_tsize = ((unsigned long) current->mm->end_code) >> PAGE_SHIFT;
dump->u_dsize = ((unsigned long) (current->mm->brk + (PAGE_SIZE-1))) >> PAGE_SHIFT;
+ up_read(&current->mm->mmap_sem);
dump->u_dsize -= dump->u_tsize;
dump->u_ssize = 0;
for (i = 0; i < 8; i++)
diff -ur 2.4/arch/m68k/kernel/process.c build-2.4/arch/m68k/kernel/process.c
--- 2.4/arch/m68k/kernel/process.c Wed Sep 19 22:39:31 2001
+++ build-2.4/arch/m68k/kernel/process.c Thu Sep 20 21:29:11 2001
@@ -291,9 +291,11 @@
dump->magic = CMAGIC;
dump->start_code = 0;
dump->start_stack = rdusp() & ~(PAGE_SIZE - 1);
+ down_read(&current->mm->mmap_sem);
dump->u_tsize = ((unsigned long) current->mm->end_code) >> PAGE_SHIFT;
dump->u_dsize = ((unsigned long) (current->mm->brk +
(PAGE_SIZE-1))) >> PAGE_SHIFT;
+ up_read(&current->mm->mmap_sem);
dump->u_dsize -= dump->u_tsize;
dump->u_ssize = 0;

diff -ur 2.4/arch/mips/kernel/process.c build-2.4/arch/mips/kernel/process.c
--- 2.4/arch/mips/kernel/process.c Wed Sep 19 22:39:31 2001
+++ build-2.4/arch/mips/kernel/process.c Thu Sep 20 21:29:34 2001
@@ -140,6 +140,7 @@
void dump_thread(struct pt_regs *regs, struct user *dump)
{
dump->magic = CMAGIC;
+ down_read(&current->mm->mmap_sem);
dump->start_code = current->mm->start_code;
dump->start_data = current->mm->start_data;
dump->start_stack = regs->regs[29] & ~(PAGE_SIZE - 1);
@@ -147,6 +148,7 @@
dump->u_dsize = (current->mm->brk + (PAGE_SIZE - 1) - dump->start_data) >> PAGE_SHIFT;
dump->u_ssize =
(current->mm->start_stack - dump->start_stack + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ up_read(&current->mm->mmap_sem);
memcpy(&dump->regs[0], regs, sizeof(struct pt_regs));
memcpy(&dump->regs[EF_SIZE/4], &current->thread.fpu, sizeof(current->thread.fpu));
}
diff -ur 2.4/arch/mips64/kernel/process.c build-2.4/arch/mips64/kernel/process.c
--- 2.4/arch/mips64/kernel/process.c Fri Feb 23 15:24:13 2001
+++ build-2.4/arch/mips64/kernel/process.c Thu Sep 20 21:29:51 2001
@@ -133,6 +133,7 @@
void dump_thread(struct pt_regs *regs, struct user *dump)
{
dump->magic = CMAGIC;
+ down_read(&current->mm->mmap_sem);
dump->start_code = current->mm->start_code;
dump->start_data = current->mm->start_data;
dump->start_stack = regs->regs[29] & ~(PAGE_SIZE - 1);
@@ -142,6 +143,7 @@
>> PAGE_SHIFT;
dump->u_ssize = (current->mm->start_stack - dump->start_stack +
PAGE_SIZE - 1) >> PAGE_SHIFT;
+ up_read(&current->mm->mmap_sem);
memcpy(&dump->regs[0], regs, sizeof(struct pt_regs));
memcpy(&dump->regs[EF_SIZE/4], &current->thread.fpu,
sizeof(current->thread.fpu));
diff -ur 2.4/arch/s390/kernel/process.c build-2.4/arch/s390/kernel/process.c
--- 2.4/arch/s390/kernel/process.c Fri Aug 17 18:24:46 2001
+++ build-2.4/arch/s390/kernel/process.c Thu Sep 20 21:30:14 2001
@@ -415,10 +415,12 @@
dump->magic = CMAGIC;
dump->start_code = 0;
dump->start_stack = regs->gprs[15] & ~(PAGE_SIZE - 1);
+ down_read(&current->mm->mmap_sem);
dump->u_tsize = ((unsigned long) current->mm->end_code) >> PAGE_SHIFT;
dump->u_dsize = ((unsigned long) (current->mm->brk + (PAGE_SIZE-1))) >> PAGE_SHIFT;
dump->u_dsize -= dump->u_tsize;
dump->u_ssize = 0;
+ up_read(&current->mm->mmap_sem);
if (dump->start_stack < TASK_SIZE)
dump->u_ssize = ((unsigned long) (TASK_SIZE - dump->start_stack)) >> PAGE_SHIFT;
memcpy(&dump->regs.gprs[0],regs,sizeof(s390_regs));
diff -ur 2.4/arch/s390x/kernel/process.c build-2.4/arch/s390x/kernel/process.c
--- 2.4/arch/s390x/kernel/process.c Fri Aug 17 18:24:46 2001
+++ build-2.4/arch/s390x/kernel/process.c Thu Sep 20 21:30:29 2001
@@ -409,10 +409,12 @@
dump->magic = CMAGIC;
dump->start_code = 0;
dump->start_stack = regs->gprs[15] & ~(PAGE_SIZE - 1);
+ down_read(&current->mm->mmap_sem);
dump->u_tsize = ((unsigned long) current->mm->end_code) >> PAGE_SHIFT;
dump->u_dsize = ((unsigned long) (current->mm->brk + (PAGE_SIZE-1))) >> PAGE_SHIFT;
dump->u_dsize -= dump->u_tsize;
dump->u_ssize = 0;
+ up_read(&current->mm->mmap_sem);
if (dump->start_stack < TASK_SIZE)
dump->u_ssize = ((unsigned long) (TASK_SIZE - dump->start_stack)) >> PAGE_SHIFT;
memcpy(&dump->regs.gprs[0],regs,sizeof(s390_regs));
diff -ur 2.4/arch/sh/kernel/process.c build-2.4/arch/sh/kernel/process.c
--- 2.4/arch/sh/kernel/process.c Wed Sep 19 22:39:32 2001
+++ build-2.4/arch/sh/kernel/process.c Thu Sep 20 21:30:47 2001
@@ -236,6 +236,7 @@
void dump_thread(struct pt_regs * regs, struct user * dump)
{
dump->magic = CMAGIC;
+ down_read(&current->mm->mmap_sem);
dump->start_code = current->mm->start_code;
dump->start_data = current->mm->start_data;
dump->start_stack = regs->regs[15] & ~(PAGE_SIZE - 1);
@@ -243,6 +244,7 @@
dump->u_dsize = (current->mm->brk + (PAGE_SIZE-1) - dump->start_data) >> PAGE_SHIFT;
dump->u_ssize = (current->mm->start_stack - dump->start_stack +
PAGE_SIZE - 1) >> PAGE_SHIFT;
+ up_read(&current->mm->mmap_sem);
/* Debug registers will come here. */

dump->regs = *regs;
diff -ur 2.4/arch/sparc/kernel/process.c build-2.4/arch/sparc/kernel/process.c
--- 2.4/arch/sparc/kernel/process.c Fri Feb 23 15:24:18 2001
+++ build-2.4/arch/sparc/kernel/process.c Thu Sep 20 21:31:28 2001
@@ -581,9 +581,11 @@
/* fuck me plenty */
memcpy(&dump->regs.regs[0], &regs->u_regs[1], (sizeof(unsigned long) * 15));
dump->uexec = current->thread.core_exec;
+ down_read(&current->mm->mmap_sem);
dump->u_tsize = (((unsigned long) current->mm->end_code) -
((unsigned long) current->mm->start_code)) & ~(PAGE_SIZE - 1);
dump->u_dsize = ((unsigned long) (current->mm->brk + (PAGE_SIZE-1)));
+ up_read(&current->mm->mmap_sem);
dump->u_dsize -= dump->u_tsize;
dump->u_dsize &= ~(PAGE_SIZE - 1);
first_stack_page = (regs->u_regs[UREG_FP] & ~(PAGE_SIZE - 1));
diff -ur 2.4/arch/sparc64/kernel/process.c build-2.4/arch/sparc64/kernel/process.c
--- 2.4/arch/sparc64/kernel/process.c Sat Jul 7 13:05:52 2001
+++ build-2.4/arch/sparc64/kernel/process.c Thu Sep 20 21:35:32 2001
@@ -699,9 +699,11 @@
dump->regs.y = regs->y;
/* fuck me plenty */
memcpy(&dump->regs.regs[0], &regs->u_regs[1], (sizeof(unsigned long) * 15));
+ down_read(&current->mm->mmap_sem);
dump->u_tsize = (((unsigned long) current->mm->end_code) -
((unsigned long) current->mm->start_code)) & ~(PAGE_SIZE - 1);
dump->u_dsize = ((unsigned long) (current->mm->brk + (PAGE_SIZE-1)));
+ up_read(&current->mm->mmap_sem);
dump->u_dsize -= dump->u_tsize;
dump->u_dsize &= ~(PAGE_SIZE - 1);
first_stack_page = (regs->u_regs[UREG_FP] & ~(PAGE_SIZE - 1));
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