[PATCH AUTOSEL 6.11 239/244] ext4: avoid use-after-free in ext4_ext_show_leaf()

Sasha Levin
2024-09-25T11:53:25Z

From: Baokun Li <libaokun1@huawei.com>

[ 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: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Tested-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://patch.msgid.link/20240822023545.1994557-5-libaokun@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ext4/extents.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index e067f2dd0335c..7954430f886d8 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3287,7 +3287,7 @@ 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)
@@ -3363,7 +3363,7 @@ 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;
}
@@ -3828,14 +3828,13 @@ 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
@@ -3932,7 +3931,7 @@ 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;
}
--
2.43.0