[PATCH v2] ocfs2: fix oob in __ocfs2_find_path

[Edward Adam Davis <eadavis@qq.com>]

Patch 2f26f58df041 modifies the definition of the array l_recs, specifying
the number of its members as l_count. In the path shown in [1], it will
first read the inode block where the system file directory is located
from the disk, and then read the l_count of each extension block from
the disk according to the extension list of the directory. Then the
value is 0 before l_count is read. If the array l_recs member is directly
accessed, the oob in [1] will be triggered.

The loop terminates when l_count is 0, similar to when next_free is 0.

[1]
UBSAN: array-index-out-of-bounds in fs/ocfs2/alloc.c:1838:11
index 0 is out of range for type 'struct ocfs2_extent_rec[] __counted_by(l_count)' (aka 'struct ocfs2_extent_rec[]')
Call Trace:
 __ocfs2_find_path+0x606/0xa40 fs/ocfs2/alloc.c:1838
 ocfs2_find_leaf+0xab/0x1c0 fs/ocfs2/alloc.c:1946
 ocfs2_get_clusters_nocache+0x172/0xc60 fs/ocfs2/extent_map.c:418
 ocfs2_get_clusters+0x505/0xa70 fs/ocfs2/extent_map.c:631
 ocfs2_extent_map_get_blocks+0x202/0x6a0 fs/ocfs2/extent_map.c:678
 ocfs2_read_virt_blocks+0x286/0x930 fs/ocfs2/extent_map.c:1001
 ocfs2_read_dir_block fs/ocfs2/dir.c:521 [inline]
 ocfs2_find_entry_el fs/ocfs2/dir.c:728 [inline]
 ocfs2_find_entry+0x3e4/0x2090 fs/ocfs2/dir.c:1120
 ocfs2_find_files_on_disk+0xdf/0x310 fs/ocfs2/dir.c:2023
 ocfs2_lookup_ino_from_name+0x52/0x100 fs/ocfs2/dir.c:2045
 _ocfs2_get_system_file_inode fs/ocfs2/sysfile.c:136 [inline]
 ocfs2_get_system_file_inode+0x326/0x770 fs/ocfs2/sysfile.c:112
 ocfs2_init_global_system_inodes+0x319/0x660 fs/ocfs2/super.c:461
 ocfs2_initialize_super fs/ocfs2/super.c:2196 [inline]
 ocfs2_fill_super+0x4432/0x65b0 fs/ocfs2/super.c:993
 get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1691
 vfs_get_tree+0x92/0x2a0 fs/super.c:1751
 fc_mount fs/namespace.c:1199 [inline]

Fixes: 2f26f58df041 ("ocfs2: annotate flexible array members with __counted_by_le()")
Reported-by: syzbot+151afab124dfbc5f15e6@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=151afab124dfbc5f15e6
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
v1 -> v2: check l_count and update comments

 fs/ocfs2/alloc.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
index 58bf58b68955..44bbc51276de 100644
--- a/fs/ocfs2/alloc.c
+++ b/fs/ocfs2/alloc.c
@@ -1812,14 +1812,16 @@ static int __ocfs2_find_path(struct ocfs2_caching_info *ci,
 			ret = -EROFS;
 			goto out;
 		}
-		if (le16_to_cpu(el->l_next_free_rec) == 0) {
+		if (le16_to_cpu(el->l_next_free_rec) == 0 ||
+		    le16_to_cpu(el->l_count) == 0) {
 			ocfs2_error(ocfs2_metadata_cache_get_super(ci),
-				    "Owner %llu has empty extent list at depth %u\n",
+				    "Owner %llu has empty extent list at depth %u "
+				    "(next free=%u count=%u)\n",
 				    (unsigned long long)ocfs2_metadata_cache_owner(ci),
-				    le16_to_cpu(el->l_tree_depth));
+				    le16_to_cpu(el->l_tree_depth),
+				    le16_to_cpu(el->l_next_free_rec), le16_to_cpu(el->l_count));
 			ret = -EROFS;
 			goto out;
-
 		}
 
 		for(i = 0; i < le16_to_cpu(el->l_next_free_rec) - 1; i++) {
-- 
2.43.0