Commit 2d9ee808 authored by Baokun Li's avatar Baokun Li
Browse files

ext4: avoid use-after-free in ext4_ext_show_leaf() 

stable inclusion
from stable-v6.6.55
commit 34b2096380ba475771971a778a478661a791aa15
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IAYR98
CVE: CVE-2024-49889

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=34b2096380ba475771971a778a478661a791aa15



--------------------------------

[ Upstream commit 4e2524ba2ca5f54bdbb9e5153bea00421ef653f5 ]

In ext4_find_extent(), path may be freed by error or be reallocated, so
using a previously saved *ppath may have been freed and thus may trigger
use-after-free, as follows:

ext4_split_extent
  path = *ppath;
  ext4_split_extent_at(ppath)
  path = ext4_find_extent(ppath)
  ext4_split_extent_at(ppath)
    // ext4_find_extent fails to free path
    // but zeroout succeeds
  ext4_ext_show_leaf(inode, path)
    eh = path[depth].p_hdr
    // path use-after-free !!!

Similar to ext4_split_extent_at(), we use *ppath directly as an input to
ext4_ext_show_leaf(). Fix a spelling error by the way.

Same problem in ext4_ext_handle_unwritten_extents(). Since 'path' is only
used in ext4_ext_show_leaf(), remove 'path' and use *ppath directly.

This issue is triggered only when EXT_DEBUG is defined and therefore does
not affect functionality.

Signed-off-by: default avatarBaokun Li <libaokun1@huawei.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Reviewed-by: default avatarOjaswin Mujoo <ojaswin@linux.ibm.com>
Tested-by: default avatarOjaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://patch.msgid.link/20240822023545.1994557-5-libaokun@huaweicloud.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
Signed-off-by: default avatarBaokun Li <libaokun1@huawei.com>
parent bc1376a3

fs/ext4/extents.c

+4 −5
Original line number Diff line number Diff line
@@ -3298,7 +3298,7 @@ static int ext4_split_extent_at(handle_t *handle, 
}



/*

 * ext4_split_extents() splits an extent and mark extent which is covered

 * ext4_split_extent() splits an extent and mark extent which is covered

 * by @map as split_flags indicates

 *

 * It may result in splitting the extent into multiple extents (up to three)
@@ -3374,7 +3374,7 @@ static int ext4_split_extent(handle_t *handle, 
			goto out;

	}



	ext4_ext_show_leaf(inode, path);

	ext4_ext_show_leaf(inode, *ppath);

out:

	return err ? err : allocated;

}
@@ -3845,14 +3845,13 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode, 
			struct ext4_ext_path **ppath, int flags,

			unsigned int allocated, ext4_fsblk_t newblock)

{

	struct ext4_ext_path __maybe_unused *path = *ppath;

	int ret = 0;

	int err = 0;



	ext_debug(inode, "logical block %llu, max_blocks %u, flags 0x%x, allocated %u\n",

		  (unsigned long long)map->m_lblk, map->m_len, flags,

		  allocated);

	ext4_ext_show_leaf(inode, path);

	ext4_ext_show_leaf(inode, *ppath);



	/*

	 * When writing into unwritten space, we should not fail to
@@ -3949,7 +3948,7 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode, 
	if (allocated > map->m_len)

		allocated = map->m_len;

	map->m_len = allocated;

	ext4_ext_show_leaf(inode, path);

	ext4_ext_show_leaf(inode, *ppath);

out2:

	return err ? err : allocated;

}