CVE-2024-26868

In the Linux kernel, the following vulnerability has been resolved: nfs:
fix panic when nfs4_ff_layout_prepare_ds() fails We’ve been seeing the
following panic in production BUG: kernel NULL pointer dereference,
address: 0000000000000065 PGD 2f485f067 P4D 2f485f067 PUD 2cc5d8067 PMD 0
RIP: 0010:ff_layout_cancel_io+0x3a/0x90 [nfs_layout_flexfiles] Call Trace:
<TASK> ? __die+0x78/0xc0 ? page_fault_oops+0x286/0x380 ?
__rpc_execute+0x2c3/0x470 [sunrpc] ? rpc_new_task+0x42/0x1c0 [sunrpc] ?
exc_page_fault+0x5d/0x110 ? asm_exc_page_fault+0x22/0x30 ?
ff_layout_free_layoutreturn+0x110/0x110 [nfs_layout_flexfiles] ?
ff_layout_cancel_io+0x3a/0x90 [nfs_layout_flexfiles] ?
ff_layout_cancel_io+0x6f/0x90 [nfs_layout_flexfiles]
pnfs_mark_matching_lsegs_return+0x1b0/0x360 [nfsv4]
pnfs_error_mark_layout_for_return+0x9e/0x110 [nfsv4] ?
ff_layout_send_layouterror+0x50/0x160 [nfs_layout_flexfiles]
nfs4_ff_layout_prepare_ds+0x11f/0x290 [nfs_layout_flexfiles]
ff_layout_pg_init_write+0xf0/0x1f0 [nfs_layout_flexfiles]
__nfs_pageio_add_request+0x154/0x6c0 [nfs]
nfs_pageio_add_request+0x26b/0x380 [nfs] nfs_do_writepage+0x111/0x1e0 [nfs]
nfs_writepages_callback+0xf/0x30 [nfs] write_cache_pages+0x17f/0x380 ?
nfs_pageio_init_write+0x50/0x50 [nfs] ? nfs_writepages+0x6d/0x210 [nfs] ?
nfs_writepages+0x6d/0x210 [nfs] nfs_writepages+0x125/0x210 [nfs]
do_writepages+0x67/0x220 ? generic_perform_write+0x14b/0x210
filemap_fdatawrite_wbc+0x5b/0x80 file_write_and_wait_range+0x6d/0xc0
nfs_file_fsync+0x81/0x170 [nfs] ? nfs_file_mmap+0x60/0x60 [nfs]
__x64_sys_fsync+0x53/0x90 do_syscall_64+0x3d/0x90
entry_SYSCALL_64_after_hwframe+0x46/0xb0 Inspecting the core with drgn I
was able to pull this >>> prog.crashed_thread().stack_trace()[0] #0 at
0xffffffffa079657a (ff_layout_cancel_io+0x3a/0x84) in ff_layout_cancel_io
at fs/nfs/flexfilelayout/flexfilelayout.c:2021:27 >>>
prog.crashed_thread().stack_trace()[0][‘idx’] (u32)1 >>>
prog.crashed_thread().stack_trace()[0][‘flseg’].mirror_array[1].mirror_ds
(struct nfs4_ff_layout_ds *)0xffffffffffffffed This is clear from the stack
trace, we call nfs4_ff_layout_prepare_ds() which could error out
initializing the mirror_ds, and then we go to clean it all up and our check
is only for if (!mirror->mirror_ds). This is inconsistent with the rest of
the users of mirror_ds, which have if (IS_ERR_OR_NULL(mirror_ds)) to keep
from tripping over this exact scenario. Fix this up in
ff_layout_cancel_io() to make sure we don’t panic when we get an error. I
also spot checked all the other instances of checking mirror_ds and we
appear to be doing the correct checks everywhere, only unconditionally
dereferencing mirror_ds when we know it would be valid.