Offering: HULK hulk inclusion category: bugfix bugzilla: https://atomgit.com/openeuler/kernel/issues/9553 ------------------------ A corrupted directory can trigger the following KASAN report when ext4_readdir() resumes from an invalid position: BUG: KASAN: use-after-free in __ext4_check_dir_entry+0x5ef/0x820 Read of size 2 at addr ffff88810a646000 by task repro_linear/509 Call Trace: <TASK> dump_stack_lvl+0x53/0x70 print_report+0xd0/0x630 kasan_report+0xce/0x100 __ext4_check_dir_entry+0x5ef/0x820 ext4_readdir+0xcde/0x2b70 iterate_dir+0x1a1/0x520 __x64_sys_getdents64+0x12b/0x220 do_syscall_64+0xf9/0x540 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK> KASAN reports use-after-free because the out-of-bounds access lands in an adjacent freed page. The directory buffer itself is still referenced. ext4_dir_llseek() invalidates the directory cookie so that ext4_readdir() rescans directory entries from the start of the block. The rescan checks only the lower bound of rec_len before advancing. A corrupted rec_len can therefore place the offset where the block has insufficient space for a complete directory entry. The rescan itself may dereference that truncated entry, or the main loop may pass it to __ext4_check_dir_entry(). The latter reads de->rec_len before validating the range. For example: block offset 0 4092 4096 |---- de1.rec_len = 4092 -----|----| de2.inode | de2.rec_len ^ OOB, reported as UAF de2 starts at offset 4092 in this 4 KiB block. Its four-byte inode fits in the block, but its rec_len starts at offset 4096 and crosses the boundary. The minimum safe length is inode-dependent. Encrypted and casefolded directory entries need eight additional hash bytes, while a valid metadata checksum tail is only 12 bytes. Cache the metadata checksum feature state and derive the minimum directory entry length from the on-disk format. Use it to bound both the rescan and the offset passed to the main loop. Report an offset in a truncated block tail and skip the remainder of the block, while continuing to accept an offset exactly at the block boundary. Reported-by: syzbot+5322c5c260eb44d209ed@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=5322c5c260eb44d209ed Fixes: ac27a0ec112a ("[PATCH] ext4: initial copy of files from ext3") Signed-off-by: Yao Kai <yaokai34@huawei.com> Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Zhang Yi <yi.zhang@huawei.com> --- fs/ext4/dir.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c index 513360234b14..c2e0b7c9562e 100644 --- a/fs/ext4/dir.c +++ b/fs/ext4/dir.c @@ -219,7 +219,9 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx) * dirent right now. Scan from the start of the block * to make sure. */ if (!inode_eq_iversion(inode, file->f_version)) { - for (i = 0; i < sb->s_blocksize && i < offset; ) { + for (i = 0; + i <= sb->s_blocksize - EXT4_DIR_REC_LEN(1) && + i < offset;) { de = (struct ext4_dir_entry_2 *) (bh->b_data + i); /* It's too expensive to do a full @@ -240,6 +242,16 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx) file->f_version = inode_query_iversion(inode); } + if (unlikely(offset < sb->s_blocksize && + offset > sb->s_blocksize - EXT4_DIR_REC_LEN(1))) { + EXT4_ERROR_FILE(file, bh->b_blocknr, + "bad entry in directory: %s - offset=%u, size=%lu", + "directory entry too close to block end", + offset, sb->s_blocksize); + ctx->pos = round_up(ctx->pos, sb->s_blocksize); + goto next_block; + } + while (ctx->pos < inode->i_size && offset < sb->s_blocksize) { de = (struct ext4_dir_entry_2 *) (bh->b_data + offset); @@ -285,6 +297,7 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx) ctx->pos += ext4_rec_len_from_disk(de->rec_len, sb->s_blocksize); } +next_block: if ((ctx->pos < inode->i_size) && !dir_relax_shared(inode)) goto done; brelse(bh); -- 2.34.1