When walking through an inode extents, the ext4_ext_binsearch_idx() function assumes that the extent header has been previously validated. However, there are no checks that verify that the number of entries (eh->eh_entries) is non-zero. And this will lead to problems because the EXT_FIRST_INDEX() and EXT_LAST_INDEX() will return garbage and result in this: [ 135.245946] ------------[ cut here ]------------ [ 135.247579] kernel BUG at fs/ext4/extents.c:2258! [ 135.249045] invalid opcode: 0000 [#1] PREEMPT SMP [ 135.250320] CPU: 2 PID: 238 Comm: tmp118 Not tainted 5.19.0-rc8+ #4 [ 135.252067] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b-rebuilt.opensuse.org 04/01/2014 [ 135.255065] RIP: 0010:ext4_ext_map_blocks+0xc20/0xcb0 [ 135.256475] Code: [ 135.261433] RSP: 0018:ffffc900005939f8 EFLAGS: 00010246 [ 135.262847] RAX: 0000000000000024 RBX: ffffc90000593b70 RCX: 0000000000000023 [ 135.264765] RDX: ffff8880038e5f10 RSI: 0000000000000003 RDI: ffff8880046e922c [ 135.266670] RBP: ffff8880046e9348 R08: 0000000000000001 R09: ffff888002ca580c [ 135.268576] R10: 0000000000002602 R11: 0000000000000000 R12: 0000000000000024 [ 135.270477] R13: 0000000000000000 R14: 0000000000000024 R15: 0000000000000000 [ 135.272394] FS: 00007fdabdc56740(0000) GS:ffff88807dd00000(0000) knlGS:0000000000000000 [ 135.274510] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 135.276075] CR2: 00007ffc26bd4f00 CR3: 0000000006261004 CR4: 0000000000170ea0 [ 135.277952] Call Trace: [ 135.278635] <TASK> [ 135.279247] ? preempt_count_add+0x6d/0xa0 [ 135.280358] ? percpu_counter_add_batch+0x55/0xb0 [ 135.281612] ? _raw_read_unlock+0x18/0x30 [ 135.282704] ext4_map_blocks+0x294/0x5a0 [ 135.283745] ? xa_load+0x6f/0xa0 [ 135.284562] ext4_mpage_readpages+0x3d6/0x770 [ 135.285646] read_pages+0x67/0x1d0 [ 135.286492] ? folio_add_lru+0x51/0x80 [ 135.287441] page_cache_ra_unbounded+0x124/0x170 [ 135.288510] filemap_get_pages+0x23d/0x5a0 [ 135.289457] ? path_openat+0xa72/0xdd0 [ 135.290332] filemap_read+0xbf/0x300 [ 135.291158] ? _raw_spin_lock_irqsave+0x17/0x40 [ 135.292192] new_sync_read+0x103/0x170 [ 135.293014] vfs_read+0x15d/0x180 [ 135.293745] ksys_read+0xa1/0xe0 [ 135.294461] do_syscall_64+0x3c/0x80 [ 135.295284] entry_SYSCALL_64_after_hwframe+0x46/0xb0 Unfortunately, __ext4_ext_check() only verifies that eh->eh_entries doesn't exceed eh->eh_max. And since an empty leaf seems to be a valid value in same cases, adding this extra check there isn't an option. This patch simply adds the check directly in ext4_ext_binsearch_idx() and propagates this error so that the kernel doesn't hit this BUG_ON() in ext4_ext_determine_hole(). Link: https://bugzilla.kernel.org/show_bug.cgi?id=215941 Signed-off-by: Luís Henriques <lhenriques@xxxxxxx> --- fs/ext4/extents.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) Hi! This bug is easily reproducible using the filesystem image provided -- it's just a matter of mounting it and run: $ cat /mnt/foo/bar/xattr Anyway, I hope my analysis of the bug is correct -- the root cause seems to be an extent header with an invalid value for in eh_entries, which will later cause the BUG_ON(). Cheers, -- Luís diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index c148bb97b527..53cfe2c681c4 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -738,7 +738,7 @@ void ext4_ext_drop_refs(struct ext4_ext_path *path) * binary search for the closest index of the given block * the header must be checked before calling this */ -static void +static int ext4_ext_binsearch_idx(struct inode *inode, struct ext4_ext_path *path, ext4_lblk_t block) { @@ -748,6 +748,11 @@ ext4_ext_binsearch_idx(struct inode *inode, ext_debug(inode, "binsearch for %u(idx): ", block); + if (eh->eh_entries == 0) { + EXT4_ERROR_INODE(inode, "No entries in extent header!"); + return -EFSCORRUPTED; + } + l = EXT_FIRST_INDEX(eh) + 1; r = EXT_LAST_INDEX(eh); while (l <= r) { @@ -791,7 +796,7 @@ ext4_ext_binsearch_idx(struct inode *inode, BUG_ON(chix != path->p_idx); } #endif - + return 0; } /* @@ -919,7 +924,9 @@ ext4_find_extent(struct inode *inode, ext4_lblk_t block, ext_debug(inode, "depth %d: num %d, max %d\n", ppos, le16_to_cpu(eh->eh_entries), le16_to_cpu(eh->eh_max)); - ext4_ext_binsearch_idx(inode, path + ppos, block); + ret = ext4_ext_binsearch_idx(inode, path + ppos, block); + if (ret < 0) + goto err; path[ppos].p_block = ext4_idx_pblock(path[ppos].p_idx); path[ppos].p_depth = i; path[ppos].p_ext = NULL;
