CVE-2024-47701: ext4: avoid OOB when system.data xattr changes underneath the filesystem

In the Linux kernel, the following vulnerability has been resolved:

ext4: avoid OOB when system.data xattr changes underneath the filesystem

When looking up for an entry in an inlined directory, if evalueoffs is changed underneath the filesystem by some change in the block device, it will lead to an out-of-bounds access that KASAN detects as an UAF.

EXT4-fs (loop0): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: none. loop0: detected capacity change from 2048 to 2047 ================================================================== BUG: KASAN: use-after-free in ext4searchdir+0xf2/0x1c0 fs/ext4/namei.c:1500 Read of size 1 at addr ffff88803e91130f by task syz-executor269/5103

CPU: 0 UID: 0 PID: 5103 Comm: syz-executor269 Not tainted 6.11.0-rc4-syzkaller #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> dumpstack lib/dumpstack.c:93 [inline] dumpstacklvl+0x241/0x360 lib/dumpstack.c:119 printaddressdescription mm/kasan/report.c:377 [inline] printreport+0x169/0x550 mm/kasan/report.c:488 kasanreport+0x143/0x180 mm/kasan/report.c:601 ext4searchdir+0xf2/0x1c0 fs/ext4/namei.c:1500 ext4findinlineentry+0x4be/0x5e0 fs/ext4/inline.c:1697 ext4findentry+0x2b4/0x1b30 fs/ext4/namei.c:1573 ext4lookupentry fs/ext4/namei.c:1727 [inline] ext4lookup+0x15f/0x750 fs/ext4/namei.c:1795 lookuponeqstrexcl+0x11f/0x260 fs/namei.c:1633 filenamecreate+0x297/0x540 fs/namei.c:3980 dosymlinkat+0xf9/0x3a0 fs/namei.c:4587 dosyssymlinkat fs/namei.c:4610 [inline] sesyssymlinkat fs/namei.c:4607 [inline] x64syssymlinkat+0x95/0xb0 fs/namei.c:4607 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0xf3/0x230 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x77/0x7f RIP: 0033:0x7f3e73ced469 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 21 18 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fff4d40c258 EFLAGS: 00000246 ORIGRAX: 000000000000010a RAX: ffffffffffffffda RBX: 0032656c69662f2e RCX: 00007f3e73ced469 RDX: 0000000020000200 RSI: 00000000ffffff9c RDI: 00000000200001c0 RBP: 0000000000000000 R08: 00007fff4d40c290 R09: 00007fff4d40c290 R10: 0023706f6f6c2f76 R11: 0000000000000246 R12: 00007fff4d40c27c R13: 0000000000000003 R14: 431bde82d7b634db R15: 00007fff4d40c2b0 </TASK>

Calling ext4xattribodyfind right after reading the inode with ext4getinodeloc will lead to a check of the validity of the xattrs, avoiding this problem.