xfs: validate cached inodes are free when allocated
A recent fuzzed filesystem image cached random dcache corruption when the reproducer was run. This often showed up as panics in lookup_slow() on a null inode->i_ops pointer when doing pathwalks. BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 .... Call Trace: lookup_slow+0x44/0x60 walk_component+0x3dd/0x9f0 link_path_walk+0x4a7/0x830 path_lookupat+0xc1/0x470 filename_lookup+0x129/0x270 user_path_at_empty+0x36/0x40 path_listxattr+0x98/0x110 SyS_listxattr+0x13/0x20 do_syscall_64+0xf5/0x280 entry_SYSCALL_64_after_hwframe+0x42/0xb7 but had many different failure modes including deadlocks trying to lock the inode that was just allocated or KASAN reports of use-after-free violations. The cause of the problem was a corrupt INOBT on a v4 fs where the root inode was marked as free in the inobt record. Hence when we allocated an inode, it chose the root inode to allocate, found it in the cache and re-initialised it. We recently fixed a similar inode allocation issue caused by inobt record corruption problem in xfs_iget_cache_miss() in commit ee457001 ("xfs: catch inode allocation state mismatch corruption"). This change adds similar checks to the cache-hit path to catch it, and turns the reproducer into a corruption shutdown situation. Reported-by: NWen Xu <wen.xu@gatech.edu> Signed-Off-By: NDave Chinner <dchinner@redhat.com> Reviewed-by: NChristoph Hellwig <hch@lst.de> Reviewed-by: NCarlos Maiolino <cmaiolino@redhat.com> Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com> [darrick: fix typos in comment] Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
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