From 84e97c2767f9ed711718b47b8722ddd137f1dfe9 Mon Sep 17 00:00:00 2001 From: Chao Yu Date: Mon, 23 Mar 2015 10:36:15 +0800 Subject: [PATCH] f2fs: avoid NULL pointer dereference in f2fs_xattr_advise_get We will encounter oops by executing below command. getfattr -n system.advise /mnt/f2fs/file Killed message log: BUG: unable to handle kernel NULL pointer dereference at (null) IP: [] f2fs_xattr_advise_get+0x29/0x40 [f2fs] *pdpt = 00000000319b7001 *pde = 0000000000000000 Oops: 0002 [#1] SMP Modules linked in: f2fs(O) snd_intel8x0 snd_ac97_codec ac97_bus snd_pcm snd_seq_midi snd_seq_midi_event snd_rawmidi snd_seq joydev snd_seq_device snd_timer bnep snd rfcomm microcode bluetooth soundcore i2c_piix4 mac_hid serio_raw parport_pc ppdev lp parport binfmt_misc hid_generic psmouse usbhid hid e1000 [last unloaded: f2fs] CPU: 3 PID: 3134 Comm: getfattr Tainted: G O 4.0.0-rc1 #6 Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006 task: f3a71b60 ti: f19a6000 task.ti: f19a6000 EIP: 0060:[] EFLAGS: 00010246 CPU: 3 EIP is at f2fs_xattr_advise_get+0x29/0x40 [f2fs] EAX: 00000000 EBX: f19a7e71 ECX: 00000000 EDX: f8b5b467 ESI: 00000000 EDI: f2008570 EBP: f19a7e14 ESP: f19a7e08 DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 CR0: 80050033 CR2: 00000000 CR3: 319b8000 CR4: 000007f0 Stack: f8b5a634 c0cbb580 00000000 f19a7e34 c1193850 00000000 00000007 f19a7e71 f19a7e64 c0cbb580 c1193810 f19a7e50 c1193c00 00000000 00000000 00000000 c0cbb580 00000000 f19a7f70 c1194097 00000000 00000000 00000000 74737973 Call Trace: [] generic_getxattr+0x40/0x50 [] ? xattr_resolve_name+0x80/0x80 [] vfs_getxattr+0x70/0xa0 [] getxattr+0x87/0x190 [] ? path_lookupat+0x57/0x5f0 [] ? putname+0x32/0x50 [] ? kmem_cache_alloc+0x2a/0x130 [] ? putname+0x32/0x50 [] ? putname+0x32/0x50 [] ? putname+0x32/0x50 [] ? user_path_at_empty+0x49/0x70 [] ? user_path_at+0x1f/0x30 [] path_getxattr+0x47/0x80 [] SyS_getxattr+0x27/0x30 [] sysenter_do_call+0x12/0x12 Code: 66 90 55 89 e5 57 56 53 66 66 66 66 90 8b 78 20 89 d3 ba 67 b4 b5 f8 89 d8 89 ce e8 42 7c 7b c8 85 c0 75 16 0f b6 87 44 01 00 00 <88> 06 b8 01 00 00 00 5b 5e 5f 5d c3 8d 76 00 b8 ea ff ff ff eb EIP: [] f2fs_xattr_advise_get+0x29/0x40 [f2fs] SS:ESP 0068:f19a7e08 CR2: 0000000000000000 ---[ end trace 860260654f1f416a ]--- The reason is that in getfattr there are two steps which is indicated by strace info: 1) try to lookup and get size of specified xattr. 2) get value of the extented attribute. strace info: getxattr("/mnt/f2fs/file", "system.advise", 0x0, 0) = 1 getxattr("/mnt/f2fs/file", "system.advise", "\x00", 256) = 1 For the first step, getfattr may pass a NULL pointer in @value and zero in @size as parameters for ->getxattr, but we access this @value pointer directly without checking whether the pointer is valid or not in f2fs_xattr_advise_get, so the oops occurs. This patch fixes this issue by verifying @value pointer before using. Signed-off-by: Chao Yu Signed-off-by: Jaegeuk Kim --- fs/f2fs/xattr.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c index 5072bf9ae0ef..55649bec0b4d 100644 --- a/fs/f2fs/xattr.c +++ b/fs/f2fs/xattr.c @@ -135,7 +135,8 @@ static int f2fs_xattr_advise_get(struct dentry *dentry, const char *name, if (strcmp(name, "") != 0) return -EINVAL; - *((char *)buffer) = F2FS_I(inode)->i_advise; + if (buffer) + *((char *)buffer) = F2FS_I(inode)->i_advise; return sizeof(char); } -- 2.11.0