fuse: fix beyond-end-of-page access in fuse_parse_cache()
With DEBUG_PAGEALLOC on, the following triggers.
BUG: unable to handle page fault for address:
ffff88859367c000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD
3001067 P4D
3001067 PUD
406d3a8067 PMD
406d30c067 PTE
800ffffa6c983060
Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
CPU: 38 PID:
3110657 Comm: python2.7
RIP: 0010:fuse_readdir+0x88f/0xe7a [fuse]
Code: 49 8b 4d 08 49 39 4e 60 0f 84 44 04 00 00 48 8b 43 08 43 8d 1c 3c 4d 01 7e 68 49 89 dc 48 03 5c 24 38 49 89 46 60 8b 44 24 30 <8b> 4b 10 44 29 e0 48 89 ca 48 83 c1 1f 48 83 e1 f8 83 f8 17 49 89
RSP: 0018:
ffffc90035edbde0 EFLAGS:
00010286
RAX:
0000000000001000 RBX:
ffff88859367bff0 RCX:
0000000000000000
RDX:
0000000000000000 RSI:
ffff88859367bfed RDI:
0000000000920907
RBP:
ffffc90035edbe90 R08:
000000000000014b R09:
0000000000000004
R10:
ffff88859367b000 R11:
0000000000000000 R12:
0000000000000ff0
R13:
ffffc90035edbee0 R14:
ffff889fb8546180 R15:
0000000000000020
FS:
00007f80b5f4a740(0000) GS:
ffff889fffa00000(0000) knlGS:
0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0:
0000000080050033
CR2:
ffff88859367c000 CR3:
0000001c170c2001 CR4:
00000000003606e0
DR0:
0000000000000000 DR1:
0000000000000000 DR2:
0000000000000000
DR3:
0000000000000000 DR6:
00000000fffe0ff0 DR7:
0000000000000400
Call Trace:
iterate_dir+0x122/0x180
__x64_sys_getdents+0xa6/0x140
do_syscall_64+0x42/0x100
entry_SYSCALL_64_after_hwframe+0x44/0xa9
It's in fuse_parse_cache(). %rbx (
ffff88859367bff0) is fuse_dirent
pointer - addr + offset. FUSE_DIRENT_SIZE() is trying to dereference
namelen off of it but that derefs into the next page which is disabled
by pagealloc debug causing a PF.
This is caused by dirent->namelen being accessed before ensuring that
there's enough bytes in the page for the dirent. Fix it by pushing
down reclen calculation.
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes:
5d7bc7e8680c ("fuse: allow using readdir cache")
Cc: stable@vger.kernel.org # v4.20+
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>