[U-Boot] [PATCH v3 01/13] ext4: fix possible crash on directory traversal, ignore deleted entries

Stefan Brüns
2016-08-28T20:42:26Z

The following command triggers a segfault in search_dir:
./sandbox/u-boot -c 'host bind 0 ./sandbox/test/fs/3GB.ext4.img ;
ext4write host 0 0 /./foo 0x10'

The following command triggers a segfault in check_filename:
./sandbox/u-boot -c 'host bind 0 ./sandbox/test/fs/3GB.ext4.img ;
ext4write host 0 0 /. 0x10'

"." is the first entry in the directory, thus previous_dir is NULL. The
whole previous_dir block in search_dir seems to be a bad copy from
check_filename(...). As the changed data is not written to disk, the
statement is mostly harmless, save the possible NULL-ptr reference.

Typically a file is unlinked by extending the direntlen of the previous
entry. If the entry is the first entry in the directory block, it is
invalidated by setting inode=0.

The inode==0 case is hard to trigger without crafted filesystems. It only
hits if the first entry in a directory block is deleted and later a lookup
for the entry (by name) is done.

Signed-off-by: Stefan Br?ns <stefan.bruens@rwth-aachen.de>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
---
fs/ext4/ext4_common.c | 58 +++++++++++++++++++--------------------------------
fs/ext4/ext4_write.c | 2 +-
include/ext4fs.h | 2 +-
3 files changed, 23 insertions(+), 39 deletions(-)

v2: Fix bad filename compare on delete, used substring only
v3: Added Reviewed-by

diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
index 4a003cf..3736533 100644
--- a/fs/ext4/ext4_common.c
+++ b/fs/ext4/ext4_common.c
@@ -528,16 +528,14 @@ fail:
static int search_dir(struct ext2_inode *parent_inode, char *dirname)
{
int status;
- int inodeno;
+ int inodeno = 0;
int totalbytes;
int templength;
int direct_blk_idx;
long int blknr;
- int found = 0;
char *ptr = NULL;
unsigned char *block_buffer = NULL;
struct ext2_dirent *dir = NULL;
- struct ext2_dirent *previous_dir = NULL;
struct ext_filesystem *fs = get_fs();

/* read the block no allocated to a file */
@@ -547,7 +545,7 @@ static int search_dir(struct ext2_inode *parent_inode, char *dirname)
if (blknr == 0)
goto fail;

- /* read the blocks of parenet inode */
+ /* read the blocks of parent inode */
block_buffer = zalloc(fs->blksz);
if (!block_buffer)
goto fail;
@@ -567,15 +565,9 @@ static int search_dir(struct ext2_inode *parent_inode, char *dirname)
* space in the block that means
* it is a last entry of directory entry
*/
- if (strlen(dirname) == dir->namelen) {
+ if (dir->inode && (strlen(dirname) == dir->namelen)) {
if (strncmp(dirname, ptr + sizeof(struct ext2_dirent), dir->namelen) == 0) {
- uint16_t new_len;
- new_len = le16_to_cpu(previous_dir->direntlen);
- new_len += le16_to_cpu(dir->direntlen);
- previous_dir->direntlen = cpu_to_le16(new_len);
inodeno = le32_to_cpu(dir->inode);
- dir->inode = 0;
- found = 1;
break;
}
}
@@ -586,19 +578,15 @@ static int search_dir(struct ext2_inode *parent_inode, char *dirname)
/* traversing the each directory entry */
templength = le16_to_cpu(dir->direntlen);
totalbytes = totalbytes + templength;
- previous_dir = dir;
dir = (struct ext2_dirent *)((char *)dir + templength);
ptr = (char *)dir;
}

- if (found == 1) {
- free(block_buffer);
- block_buffer = NULL;
- return inodeno;
- }
-
free(block_buffer);
block_buffer = NULL;
+
+ if (inodeno > 0)
+ return inodeno;
}

fail:
@@ -774,15 +762,13 @@ fail:
return result_inode_no;
}

-static int check_filename(char *filename, unsigned int blknr)
+static int unlink_filename(char *filename, unsigned int blknr)
{
- unsigned int first_block_no_of_root;
int totalbytes = 0;
int templength = 0;
int status, inodeno;
int found = 0;
char *root_first_block_buffer = NULL;
- char *root_first_block_addr = NULL;
struct ext2_dirent *dir = NULL;
struct ext2_dirent *previous_dir = NULL;
char *ptr = NULL;
@@ -790,18 +776,15 @@ static int check_filename(char *filename, unsigned int blknr)
int ret = -1;

/* get the first block of root */
- first_block_no_of_root = blknr;
root_first_block_buffer = zalloc(fs->blksz);
if (!root_first_block_buffer)
return -ENOMEM;
- root_first_block_addr = root_first_block_buffer;
- status = ext4fs_devread((lbaint_t)first_block_no_of_root *
- fs->sect_perblk, 0,
+ status = ext4fs_devread((lbaint_t)blknr * fs->sect_perblk, 0,
fs->blksz, root_first_block_buffer);
if (status == 0)
goto fail;

- if (ext4fs_log_journal(root_first_block_buffer, first_block_no_of_root))
+ if (ext4fs_log_journal(root_first_block_buffer, blknr))
goto fail;
dir = (struct ext2_dirent *)root_first_block_buffer;
ptr = (char *)dir;
@@ -813,19 +796,21 @@ static int check_filename(char *filename, unsigned int blknr)
* is free availble space in the block that
* means it is a last entry of directory entry
*/
- if (strlen(filename) == dir->namelen) {
- if (strncmp(filename, ptr + sizeof(struct ext2_dirent),
- dir->namelen) == 0) {
+ if (dir->inode && (strlen(filename) == dir->namelen) &&
+ (strncmp(ptr + sizeof(struct ext2_dirent),
+ filename, dir->namelen) == 0)) {
+ printf("file found, deleting\n");
+ inodeno = le32_to_cpu(dir->inode);
+ if (previous_dir) {
uint16_t new_len;
- printf("file found deleting\n");
new_len = le16_to_cpu(previous_dir->direntlen);
new_len += le16_to_cpu(dir->direntlen);
previous_dir->direntlen = cpu_to_le16(new_len);
- inodeno = le32_to_cpu(dir->inode);
+ } else {
dir->inode = 0;
- found = 1;
- break;
}
+ found = 1;
+ break;
}

if (fs->blksz - totalbytes == le16_to_cpu(dir->direntlen))
@@ -841,8 +826,7 @@ static int check_filename(char *filename, unsigned int blknr)

if (found == 1) {
- if (ext4fs_put_metadata(root_first_block_addr,
- first_block_no_of_root))
+ if (ext4fs_put_metadata(root_first_block_buffer, blknr))
goto fail;
ret = inodeno;
}
@@ -852,7 +836,7 @@ fail:
return ret;
}

-int ext4fs_filename_check(char *filename)
+int ext4fs_filename_unlink(char *filename)
{
short direct_blk_idx = 0;
long int blknr = -1;
@@ -864,7 +848,7 @@ int ext4fs_filename_check(char *filename)
blknr = read_allocated_block(g_parent_inode, direct_blk_idx);
if (blknr == 0)
break;
- inodeno = check_filename(filename, blknr);
+ inodeno = unlink_filename(filename, blknr);
if (inodeno != -1)
return inodeno;
}
diff --git a/fs/ext4/ext4_write.c b/fs/ext4/ext4_write.c
index 3194595..70a3b5b 100644
--- a/fs/ext4/ext4_write.c
+++ b/fs/ext4/ext4_write.c
@@ -882,7 +882,7 @@ int ext4fs_write(const char *fname, unsigned char *buffer,
if (ext4fs_iget(parent_inodeno, g_parent_inode))
goto fail;
/* check if the filename is already present in root */
- existing_file_inodeno = ext4fs_filename_check(filename);
+ existing_file_inodeno = ext4fs_filename_unlink(filename);
if (existing_file_inodeno != -1) {
ret = ext4fs_delete_file(existing_file_inodeno);
fs->first_pass_bbmap = 0;
diff --git a/include/ext4fs.h b/include/ext4fs.h
index 13d2c56..e3f6216 100644
--- a/include/ext4fs.h
+++ b/include/ext4fs.h
@@ -124,7 +124,7 @@ extern int gindex;

int ext4fs_init(void);
void ext4fs_deinit(void);
-int ext4fs_filename_check(char *filename);
+int ext4fs_filename_unlink(char *filename);
int ext4fs_write(const char *fname, unsigned char *buffer,
unsigned long sizebytes);
int ext4_write_file(const char *filename, void *buf, loff_t offset, loff_t len,
--
2.9.3