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 --- fs/ext4/ext4_common.c | 57 ++++++++++++++++++--------------------------------- fs/ext4/ext4_write.c | 2 +- include/ext4fs.h | 2 +- 3 files changed, 22 insertions(+), 39 deletions(-)
diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c index b00b84f..16c5f53 100644 --- a/fs/ext4/ext4_common.c +++ b/fs/ext4/ext4_common.c @@ -511,16 +511,14 @@ 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 */ @@ -530,7 +528,7 @@ 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; @@ -550,15 +548,9 @@ 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; } } @@ -569,19 +561,15 @@ 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: @@ -757,15 +745,13 @@ 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; @@ -773,18 +759,15 @@ 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; @@ -796,19 +779,20 @@ 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 && (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)) @@ -824,8 +808,7 @@ 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; } @@ -835,7 +818,7 @@ fail: return ret; }
-int ext4fs_filename_check(char *filename) +int ext4fs_filename_unlink(char *filename) { short direct_blk_idx = 0; long int blknr = -1; @@ -847,7 +830,7 @@ 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 d03d692..f5811aa 100644 --- a/fs/ext4/ext4_write.c +++ b/fs/ext4/ext4_write.c @@ -865,7 +865,7 @@ 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,