Messages in this thread Patch in this message | | | Subject | Re: [SYSFS] Kernel Null pointer dereference in sysfs_readdir() | From | Steven Rostedt <> | Date | Wed, 12 Jul 2006 10:06:19 -0400 |
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[ added Patrick since his name is on the sysfs documentation ] [ added Andrew since I am including a patch for 2.6.18 ]
On Wed, 2006-07-12 at 14:39 +0200, Duetsch, Thomas LDE1 wrote: > Steven Rostedt wrote: > > On Wed, 2006-07-12 at 13:35 +0200, Duetsch, Thomas LDE1 wrote: > >> Hi, > >> > >> I'm currently working on a custom kernel based on Ingo's -rt patch > >> (2.6.16-rt29). > >> > >> While rebooting my machine, I came across a kernel null pointer > >> dereference in this code segment in fs/sysfs/dir.c, function > >> sysfs_readdir(): > >> > >> for (p=q->next; p!= &parent_sd->s_children; p=p->next) { > struct > >> sysfs_dirent *next; const char * name; > >> int len; > >> > >> next = list_entry(p, struct sysfs_dirent, > >> s_sibling); > >> if (!next->s_element) > >> continue; > >> > >> name = sysfs_get_name(next); > >> len = strlen(name); > >> if (next->s_dentry) > >> PROBLEM -> ino = next->s_dentry->d_inode->i_ino; > >> else > >> ino = iunique(sysfs_sb, 2); > >> > > > > Hi Thomas, > > > > Do you have a backtrace to look at? It might be helpful to see what > > functions brought us to this point. Also it might help to determine if > > the problem is vanilla, -rt, or the custom kernel. > > > > Thanks, > > > > -- Steve > > Of course, here you go: > > <1>BUG: Unable to handle kernel NULL pointer dereference at virtual > address 00000020 > <1> printing eip: > <4>c01af187 > <1>*pde = 00000000 > <0>Oops: 0000 [#1] > <0>PREEMPT > <4>cpu=0 current find:2667 > <4>current resource_set: 0 > <4> [<c0103fb1>] show_trace+0x21/0x30 (20) > <4> [<c01040ee>] dump_stack+0x1e/0x30 (20) > <4> [<c01044ca>] die+0xba/0x1b0 (68) > <4> [<c01146ed>] do_page_fault+0x37d/0x6d0 (96) > <4> [<c0103b0b>] error_code+0x4f/0x54 (120) > <4> [<c0182a60>] vfs_readdir+0xa0/0xc0 (36) > <4> [<c0182e85>] sys_getdents64+0x75/0xd0 (64) > <4> [<c0102fd9>] syscall_call+0x7/0xb (-8116) > <4>Modules linked in: ide_dump diskdump ipv6 eeprom adm1021 hwmon > i2c_piix4 i2c_core NPCI pcnet32 e100 unix > <0>CPU: 0 > <4>EIP: 0060:[<c01af187>] Tainted: P VLI > <4>EFLAGS: 00010286 (2.6.16-rt29-rs_1.0 #1) > <0>EIP is at sysfs_readdir+0xd7/0x240 > <0>eax: 00000000 ebx: cfd095a0 ecx: 00000005 edx: cf02be88 > <0>esi: cfd0959c edi: ce150c16 ebp: c35b5f50 esp: c35b5f14 > <0>ds: 007b es: 007b ss: 0068 preempt: 00000001 > <0>Process find (pid: 2667, threadinfo=c35b4000 task=c3686730 > wchan=00000000) stack_left=7900 worst_left=-1) > <0>Stack: <0>cfd0959c c3618e60 00000004 00000003 00000000 00000d74 > 00000004 cfe46a58 > <0> 00000005 ce150c10 cf02bb68 cfe46a4c ca844f20 fffffffe cfe47e40 > c35b5f74 > <0> c0182a60 ca844f20 c35b5f98 c0182d20 cfe47ec8 00001000 ca844f20 > c0182d20 > <0>Call Trace: > <4>cpu=0 current find:2667 > <4>current resource_set: 0 > <0> [<c010406a>] show_stack_log_lvl+0xaa/0xe0 (32) > <0> [<c01042ca>] show_registers+0x1ca/0x250 (64) > <0> [<c0104508>] die+0xf8/0x1b0 (68) > <0> [<c01146ed>] do_page_fault+0x37d/0x6d0 (96) > <0> [<c0103b0b>] error_code+0x4f/0x54 (120) > <0> [<c0182a60>] vfs_readdir+0xa0/0xc0 (36) > <0> [<c0182e85>] sys_getdents64+0x75/0xd0 (64) > <0> [<c0102fd9>] syscall_call+0x7/0xb (-8116) > <0>Code: 8d 74 26 00 89 34 24 e8 68 e4 ff ff 89 45 e8 b9 ff ff ff ff 31 > c0 8b 7d e8 f2 ae f7 d1 49 89 4d e4 8b 46 20 85 c0 74 74 8b 40 20 <8b> > 50 20 > 0f b7 46 1c 89 54 24 14 8b 4d 08 c1 e8 0c 89 44 24 18 > > I hope that helps, >
I believe I found the race. Here's the problem:
There's no real protection in the sysfs_readdir regarding that for loop. So the if statement
if (next->s_dentry) ino = next->s_dentry->d_inode->i_ino;
has the race.
We _can_ have a s_dentry without a d_inode! Reason is that in attaching an attribute we have: in fs/sysfs/dir.c sysfs_attach_attr()
sd->s_dentry = dentry; error = sysfs_create(dentry, (attr->mode & S_IALLUGO) | S_IFREG, init);
Where the dentry->d_inode can be NULL. I don't see any protection in this code to prevent this from happening.
Now the question is, is it safe to add the test for s_dentry->d_inode too. I ask this because the s_dentry is in the process of being filled, and I don't know what effect this will have on what readdir wants. I guess it may be safe, so I'm giving this patch:
-- Steve
Description:
In the process of creating a sysfs attribute, we can have a state where the sysfs descriptor can have a dentry with a NULL inode.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Index: linux-2.6.18-rc1/fs/sysfs/dir.c =================================================================== --- linux-2.6.18-rc1.orig/fs/sysfs/dir.c 2006-07-12 09:43:10.000000000 -0400 +++ linux-2.6.18-rc1/fs/sysfs/dir.c 2006-07-12 10:01:18.000000000 -0400 @@ -445,7 +445,7 @@ static int sysfs_readdir(struct file * f name = sysfs_get_name(next); len = strlen(name); - if (next->s_dentry) + if (next->s_dentry && next->s_dentry->d_inode) ino = next->s_dentry->d_inode->i_ino; else ino = iunique(sysfs_sb, 2);
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