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Subject[PATCH] parisc: fix bug in compat_arch_ptrace
Date
This commit in 2.6.28-rc:
81e192d6ce303b6792aa38ff35f41a1a7357f23a
parisc: convert to generic compat_sys_ptrace

introduced a bug which segfaults the parisc 64bit kernel
when stracing 32bit applications:

Kernel Fault: Code=15 regs=00000000bafa42b0 (Addr=00000001baf5ab57)
YZrvWESTHLNXBCVMcbcbcbcbOGFRQPDI
PSW: 00001000000001101111111100001011 Tainted: G W
r00-03 000000ff0806ff0b 000000004068edc0 00000000401203f8 00000000fb3e2508
r04-07 0000000040686dc0 00000000baf5a800 fffffffffffffffc fffffffffb3e2508
r08-11 00000000baf5a800 000000000004b068 00000000000402b0 0000000000040d68
r12-15 0000000000042a9c 0000000000040a9c 0000000000040d60 0000000000042e9c
r16-19 000000000004b060 000000000004b058 0000000000042d9c ffffffffffffffff
r20-23 000000000800000b 0000000000000000 000000000800000b fffffffffb3e2508
r24-27 00000000fffffffc 0000000000000003 00000000fffffffc 0000000040686dc0
r28-31 00000001baf5a7ff 00000000bafa4280 00000000bafa42b0 00000000000001d7
sr00-03 0000000000fca000 0000000000000000 0000000000000000 0000000000fca000
sr04-07 0000000000000000 0000000000000000 0000000000000000 0000000000000000

IASQ: 0000000000000000 0000000000000000 IAOQ: 0000000040120400 0000000040120404
IIR: 4b9a06b0 ISR: 0000000000000000 IOR: 00000001baf5ab57
CPU: 0 CR30: 00000000bafa4000 CR31: 00000000d22344e0
ORIG_R28: 00000000fb3e2248
IAOQ[0]: compat_arch_ptrace+0xb8/0x160
IAOQ[1]: compat_arch_ptrace+0xbc/0x160
RP(r2): compat_arch_ptrace+0xb0/0x160
Backtrace:
[<00000000401612ac>] compat_sys_ptrace+0x15c/0x180
[<0000000040104ef8>] syscall_exit+0x0/0x14

Problem is, that compat_arch_ptrace() enters with an addr value of type
compat_ulong_t and calls translate_usr_offset() to translate the
address offset into a struct pt_regs offset like this:
addr = translate_usr_offset(addr)
This means, any return value of translate_usr_offset() is
stored back as compat_ulong_t type into the addr variable.

But since translate_usr_offset() returns -1 for invalid offsets,
addr can now get the value 0xffffffff which then fails the next
return-value sanity check and thus the kernel tries to access
invalid memory:
if (addr < 0)
break;

Fix this bug by modifying translate_usr_offset() to take and return
values of type compat_ulong_t, and by returning the value
"sizeof(struct pt_regs)" as an error indicator.
Additionally change the sanity check to check for return values
for >= sizeof(struct pt_regs).

This patch survived my compile and run-tests.

Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/arch/parisc/kernel/ptrace.c b/arch/parisc/kernel/ptrace.c
index 90904f9..927db36 100644
--- a/arch/parisc/kernel/ptrace.c
+++ b/arch/parisc/kernel/ptrace.c
@@ -183,10 +183,10 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
* being 64 bit in both cases.
*/

-static long translate_usr_offset(long offset)
+static compat_ulong_t translate_usr_offset(compat_ulong_t offset)
{
if (offset < 0)
- return -1;
+ return sizeof(struct pt_regs);
else if (offset <= 32*4) /* gr[0..31] */
return offset * 2 + 4;
else if (offset <= 32*4+32*8) /* gr[0..31] + fr[0..31] */
@@ -194,7 +194,7 @@ static long translate_usr_offset(long offset)
else if (offset < sizeof(struct pt_regs)/2 + 32*4)
return offset * 2 + 4 - 32*8;
else
- return -1;
+ return sizeof(struct pt_regs);
}

long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
@@ -209,7 +209,7 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
if (addr & (sizeof(compat_uint_t)-1))
break;
addr = translate_usr_offset(addr);
- if (addr < 0)
+ if (addr >= sizeof(struct pt_regs))
break;

tmp = *(compat_uint_t *) ((char *) task_regs(child) + addr);
@@ -236,7 +236,7 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
if (addr & (sizeof(compat_uint_t)-1))
break;
addr = translate_usr_offset(addr);
- if (addr < 0)
+ if (addr >= sizeof(struct pt_regs))
break;
if (addr >= PT_FR0 && addr <= PT_FR31 + 4) {
/* Special case, fp regs are 64 bits anyway */

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