[f2fs-dev] [PATCH v2] f2fs: fix to do sanity check correctly on i_inline_xattr_size

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

syzbot reported an out-of-range access issue as below:

UBSAN: array-index-out-of-bounds in fs/f2fs/f2fs.h:3292:19
index 18446744073709550491 is out of range for type '__le32[923]' (aka 'unsigned int[923]')
CPU: 0 UID: 0 PID: 5338 Comm: syz.0.0 Not tainted 6.12.0-syzkaller-10689-g7af08b57bcb9 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 ubsan_epilogue lib/ubsan.c:231 [inline]
 __ubsan_handle_out_of_bounds+0x121/0x150 lib/ubsan.c:429
 read_inline_xattr+0x273/0x280
 lookup_all_xattrs fs/f2fs/xattr.c:341 [inline]
 f2fs_getxattr+0x57b/0x13b0 fs/f2fs/xattr.c:533
 vfs_getxattr_alloc+0x472/0x5c0 fs/xattr.c:393
 ima_read_xattr+0x38/0x60 security/integrity/ima/ima_appraise.c:229
 process_measurement+0x117a/0x1fb0 security/integrity/ima/ima_main.c:353
 ima_file_check+0xd9/0x120 security/integrity/ima/ima_main.c:572
 security_file_post_open+0xb9/0x280 security/security.c:3121
 do_open fs/namei.c:3830 [inline]
 path_openat+0x2ccd/0x3590 fs/namei.c:3987
 do_file_open_root+0x3a7/0x720 fs/namei.c:4039
 file_open_root+0x247/0x2a0 fs/open.c:1382
 do_handle_open+0x85b/0x9d0 fs/fhandle.c:414
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

index: 18446744073709550491 (decimal, unsigned long long)
= 0xfffffffffffffb9b (hexadecimal) = -1125 (decimal, long long)
UBSAN detects that inline_xattr_addr() tries to access .i_addr[-1125].

w/ below testcase, it can reproduce this bug easily:
- mkfs.f2fs -f -O extra_attr,flexible_inline_xattr /dev/sdb
- mount -o inline_xattr_size=512 /dev/sdb /mnt/f2fs
- touch /mnt/f2fs/file
- umount /mnt/f2fs
- inject.f2fs --node --mb i_inline --nid 4 --val 0x1 /dev/sdb
- inject.f2fs --node --mb i_inline_xattr_size --nid 4 --val 2048 /dev/sdb
- mount /dev/sdb /mnt/f2fs
- getfattr /mnt/f2fs/file

The root cause is if metadata of filesystem and inode were fuzzed as below:
- extra_attr feature is enabled
- flexible_inline_xattr feature is enabled
- ri.i_inline_xattr_size = 2048
- F2FS_EXTRA_ATTR bit in ri.i_inline was not set

sanity_check_inode() will skip doing sanity check on fi->i_inline_xattr_size,
result in using invalid inline_xattr_size later incorrectly, fix it.

Meanwhile, let's fix to check lower boundary for .i_inline_xattr_size w/
MIN_INLINE_XATTR_SIZE like we did in parse_options().

There is a related issue reported by syzbot, Qasim Ijaz has anlyzed and
fixed it w/ very similar way [1], as discussed, we all agree that it will
be better to do sanity check in sanity_check_inode() for fix, so finally,
let's fix these two related bugs w/ current patch.

Including commit message from Qasim's patch as below, thanks a lot for
his contribution.

"In f2fs_getxattr(), the function lookup_all_xattrs() allocates a 12-byte
(base_size) buffer for an inline extended attribute. However, when
__find_inline_xattr() calls __find_xattr(), it uses the macro
"list_for_each_xattr(entry, addr)", which starts by calling
XATTR_FIRST_ENTRY(addr). This skips a 24-byte struct f2fs_xattr_header
at the beginning of the buffer, causing an immediate out-of-bounds read
in a 12-byte allocation. The subsequent !IS_XATTR_LAST_ENTRY(entry)
check then dereferences memory outside the allocated region, triggering
the slab-out-of bounds read.

This patch prevents the out-of-bounds read by adding a check to bail
out early if inline_size is too small and does not account for the
header plus the 4-byte value that IS_XATTR_LAST_ENTRY reads."

[1]: https://lore.kernel.org/linux-f2fs-devel/Z32y1rfBY9Qb5ZjM@qasdev.system/

Fixes: 6afc662e68b5 ("f2fs: support flexible inline xattr size")
Reported-by: syzbot+69f5379a1717a0b982a1@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-f2fs-devel/674f4e7d.050a0220.17bd51.004f.GAE@google.com
Reported-by: syzbot <syzbot+f5e74075e096e757bdbf@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=f5e74075e096e757bdbf
Tested-by: syzbot <syzbot+f5e74075e096e757bdbf@syzkaller.appspotmail.com>
Tested-by: Qasim Ijaz <qasdev00@gmail.com>
Signed-off-by: Chao Yu <chao@kernel.org>
---
v2:
- including commit message from Qasim's patch.
 fs/f2fs/inode.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 282fd320bdb3..7de33da8b3ea 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -302,15 +302,6 @@ static bool sanity_check_inode(struct inode *inode, struct page *node_page)
 				  F2FS_TOTAL_EXTRA_ATTR_SIZE);
 			return false;
 		}
-		if (f2fs_sb_has_flexible_inline_xattr(sbi) &&
-			f2fs_has_inline_xattr(inode) &&
-			(!fi->i_inline_xattr_size ||
-			fi->i_inline_xattr_size > MAX_INLINE_XATTR_SIZE)) {
-			f2fs_warn(sbi, "%s: inode (ino=%lx) has corrupted i_inline_xattr_size: %d, max: %lu",
-				  __func__, inode->i_ino, fi->i_inline_xattr_size,
-				  MAX_INLINE_XATTR_SIZE);
-			return false;
-		}
 		if (f2fs_sb_has_compression(sbi) &&
 			fi->i_flags & F2FS_COMPR_FL &&
 			F2FS_FITS_IN_INODE(ri, fi->i_extra_isize,
@@ -320,6 +311,16 @@ static bool sanity_check_inode(struct inode *inode, struct page *node_page)
 		}
 	}
 
+	if (f2fs_sb_has_flexible_inline_xattr(sbi) &&
+		f2fs_has_inline_xattr(inode) &&
+		(fi->i_inline_xattr_size < MIN_INLINE_XATTR_SIZE ||
+		fi->i_inline_xattr_size > MAX_INLINE_XATTR_SIZE)) {
+		f2fs_warn(sbi, "%s: inode (ino=%lx) has corrupted i_inline_xattr_size: %d, min: %lu, max: %lu",
+			  __func__, inode->i_ino, fi->i_inline_xattr_size,
+			  MIN_INLINE_XATTR_SIZE, MAX_INLINE_XATTR_SIZE);
+		return false;
+	}
+
 	if (!f2fs_sb_has_extra_attr(sbi)) {
 		if (f2fs_sb_has_project_quota(sbi)) {
 			f2fs_warn(sbi, "%s: corrupted inode ino=%lx, wrong feature flag: %u, run fsck to fix.",
-- 
2.48.0.rc2.279.g1de40edade-goog



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