If nilfs2 reads a corrupted disk image and tries to reads a b-tree node block by calling __nilfs_btree_get_block() against an invalid virtual block address, it returns -ENOENT because conversion of the virtual block address to a disk block address fails. However, this return value is the same as the internal code that b-tree lookup routines return to indicate that the block being searched does not exist, so functions that operate on that b-tree may misbehave. When nilfs_btree_insert() receives this spurious 'not found' code from nilfs_btree_do_lookup(), it misunderstands that the 'not found' check was successful and continues the insert operation using incomplete lookup path data, causing the following crash: general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f] ... RIP: 0010:nilfs_btree_get_nonroot_node fs/nilfs2/btree.c:418 [inline] RIP: 0010:nilfs_btree_prepare_insert fs/nilfs2/btree.c:1077 [inline] RIP: 0010:nilfs_btree_insert+0x6d3/0x1c10 fs/nilfs2/btree.c:1238 Code: bc 24 80 00 00 00 4c 89 f8 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 ff e8 4b 02 92 fe 4d 8b 3f 49 83 c7 28 4c 89 f8 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 ff e8 2e 02 92 fe 4d 8b 3f 49 83 c7 02 ... Call Trace: <TASK> nilfs_bmap_do_insert fs/nilfs2/bmap.c:121 [inline] nilfs_bmap_insert+0x20d/0x360 fs/nilfs2/bmap.c:147 nilfs_get_block+0x414/0x8d0 fs/nilfs2/inode.c:101 __block_write_begin_int+0x54c/0x1a80 fs/buffer.c:1991 __block_write_begin fs/buffer.c:2041 [inline] block_write_begin+0x93/0x1e0 fs/buffer.c:2102 nilfs_write_begin+0x9c/0x110 fs/nilfs2/inode.c:261 generic_perform_write+0x2e4/0x5e0 mm/filemap.c:3772 __generic_file_write_iter+0x176/0x400 mm/filemap.c:3900 generic_file_write_iter+0xab/0x310 mm/filemap.c:3932 call_write_iter include/linux/fs.h:2186 [inline] new_sync_write fs/read_write.c:491 [inline] vfs_write+0x7dc/0xc50 fs/read_write.c:584 ksys_write+0x177/0x2a0 fs/read_write.c:637 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd ... </TASK> This patch fixes the root cause of this problem by replacing the error code that __nilfs_btree_get_block() returns on block address conversion failure from -ENOENT to another internal code -EINVAL which means that the b-tree metadata is corrupted. By returning -EINVAL, it propagates without glitches, and for all relevant b-tree operations, functions in the upper bmap layer output an error message indicating corrupted b-tree metadata via nilfs_bmap_convert_error(), and code -EIO will be eventually returned as it should be. Link: https://lkml.kernel.org/r/000000000000bd89e205f0e38355@xxxxxxxxxx Reported-by: syzbot+ede796cecd5296353515@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx> Tested-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx --- Hi Andrew, please apply this bugfix. This fixes the kernel crash above for corrupted disk images like the one syzbot produced, and presumably fixes some unexpected WARN_ONs on nilfs2 as well (which I will continue to investigate). Thanks, Ryusuke Konishi fs/nilfs2/btree.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/fs/nilfs2/btree.c b/fs/nilfs2/btree.c index b9d15c3df3cc..40ce92a332fe 100644 --- a/fs/nilfs2/btree.c +++ b/fs/nilfs2/btree.c @@ -480,9 +480,18 @@ static int __nilfs_btree_get_block(const struct nilfs_bmap *btree, __u64 ptr, ret = nilfs_btnode_submit_block(btnc, ptr, 0, REQ_OP_READ, &bh, &submit_ptr); if (ret) { - if (ret != -EEXIST) - return ret; - goto out_check; + if (likely(ret == -EEXIST)) + goto out_check; + if (ret == -ENOENT) { + /* + * Block address translation failed due to invalid + * value of 'ptr'. In this case, return internal code + * -EINVAL (broken bmap) to notify bmap layer of fatal + * metadata corruption. + */ + ret = -EINVAL; + } + return ret; } if (ra) { -- 2.34.1
