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ext4: fix possible crash on directory traversal, ignore deleted entries

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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 Brüns <stefan.bruens@rwth-aachen.de>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
master
Stefan Brüns 8 years ago committed by Tom Rini
parent 011bc3342a
commit 76a29519ff
3 changed files with 23 additions and 39 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
Show Stats Download Patch File Download Diff File
  1. 58
      fs/ext4/ext4_common.c
  2. 2
      fs/ext4/ext4_write.c
  3. 2
      include/ext4fs.h

58
fs/ext4/ext4_common.c
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@ -533,16 +533,14 @@ 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 */
@ -552,7 +550,7 @@ 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;
@ -572,15 +570,9 @@ 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;
}
}
@ -591,19 +583,15 @@ 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:
@ -779,15 +767,13 @@ 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;
@ -795,18 +781,15 @@ 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;
@ -818,19 +801,21 @@ 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))
@ -846,8 +831,7 @@ 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;
}
@ -857,7 +841,7 @@ fail:
return ret;
}
int ext4fs_filename_check(char *filename)
int ext4fs_filename_unlink(char *filename)
{
short direct_blk_idx = 0;
long int blknr = -1;
@ -869,7 +853,7 @@ 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;
}

2
fs/ext4/ext4_write.c
Unescape View File

@ -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;

2
include/ext4fs.h
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@ -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,

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