From 42cb447410d024e9d54139ae9c21ea132a8c384c Mon Sep 17 00:00:00 2001 From: yangerkun Date: Tue, 14 Sep 2021 19:14:15 +0800 Subject: [PATCH] ext4: fix potential infinite loop in ext4_dx_readdir() When ext4_htree_fill_tree() fails, ext4_dx_readdir() can run into an infinite loop since if info->last_pos != ctx->pos this will reset the directory scan and reread the failing entry. For example: 1. a dx_dir which has 3 block, block 0 as dx_root block, block 1/2 as leaf block which own the ext4_dir_entry_2 2. block 1 read ok and call_filldir which will fill the dirent and update the ctx->pos 3. block 2 read fail, but we has already fill some dirent, so we will return back to userspace will a positive return val(see ksys_getdents64) 4. the second ext4_dx_readdir will reset the world since info->last_pos != ctx->pos, and will also init the curr_hash which pos to block 1 5. So we will read block1 too, and once block2 still read fail, we can only fill one dirent because the hash of the entry in block1(besides the last one) won't greater than curr_hash 6. this time, we forget update last_pos too since the read for block2 will fail, and since we has got the one entry, ksys_getdents64 can return success 7. Latter we will trapped in a loop with step 4~6 Cc: stable@kernel.org Signed-off-by: yangerkun Reviewed-by: Jan Kara Signed-off-by: Theodore Ts'o Link: https://lore.kernel.org/r/20210914111415.3921954-1-yangerkun@huawei.com --- fs/ext4/dir.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c index ffb295aa891c0..74b172a4adda3 100644 --- a/fs/ext4/dir.c +++ b/fs/ext4/dir.c @@ -551,7 +551,7 @@ static int ext4_dx_readdir(struct file *file, struct dir_context *ctx) struct dir_private_info *info = file->private_data; struct inode *inode = file_inode(file); struct fname *fname; - int ret; + int ret = 0; if (!info) { info = ext4_htree_create_dir_info(file, ctx->pos); @@ -599,7 +599,7 @@ static int ext4_dx_readdir(struct file *file, struct dir_context *ctx) info->curr_minor_hash, &info->next_hash); if (ret < 0) - return ret; + goto finished; if (ret == 0) { ctx->pos = ext4_get_htree_eof(file); break; @@ -630,7 +630,7 @@ static int ext4_dx_readdir(struct file *file, struct dir_context *ctx) } finished: info->last_pos = ctx->pos; - return 0; + return ret < 0 ? ret : 0; } static int ext4_release_dir(struct inode *inode, struct file *filp) -- 2.39.5