| CVE: CVE-2021-41072 |
| Upstream-Status: Backport [https://github.com/plougher/squashfs-tools/commit/e048580] |
| |
| Update on 20211109: |
| Squash a follow-up fix for CVE-2021-41072 from upstream: |
| https://github.com/plougher/squashfs-tools/commit/19fcc93 |
| |
| Signed-off-by: Kai Kang <kai.kang@windriver.com> |
| |
| From e0485802ec72996c20026da320650d8362f555bd Mon Sep 17 00:00:00 2001 |
| From: Phillip Lougher <phillip@squashfs.org.uk> |
| Date: Sun, 12 Sep 2021 23:50:06 +0100 |
| Subject: [PATCH] Unsquashfs: additional write outside destination directory |
| exploit fix |
| |
| An issue on github (https://github.com/plougher/squashfs-tools/issues/72) |
| showed how some specially crafted Squashfs filesystems containing |
| invalid file names (with '/' and '..') can cause Unsquashfs to write |
| files outside of the destination directory. |
| |
| Since then it has been shown that specially crafted Squashfs filesystems |
| that contain a symbolic link pointing outside of the destination directory, |
| coupled with an identically named file within the same directory, can |
| cause Unsquashfs to write files outside of the destination directory. |
| |
| Specifically the symbolic link produces a pathname pointing outside |
| of the destination directory, which is then followed when writing the |
| duplicate identically named file within the directory. |
| |
| This commit fixes this exploit by explictly checking for duplicate |
| filenames within a directory. As directories in v2.1, v3.x, and v4.0 |
| filesystems are sorted, this is achieved by checking for consecutively |
| identical filenames. Additionally directories are checked to |
| ensure they are sorted, to avoid attempts to evade the duplicate |
| check. |
| |
| Version 1.x and 2.0 filesystems (where the directories were unsorted) |
| are sorted and then the above duplicate filename check is applied. |
| |
| Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk> |
| --- |
| squashfs-tools/Makefile | 6 +- |
| squashfs-tools/unsquash-1.c | 6 ++ |
| squashfs-tools/unsquash-12.c | 110 +++++++++++++++++++++++++++++++++ |
| squashfs-tools/unsquash-1234.c | 21 +++++++ |
| squashfs-tools/unsquash-2.c | 16 +++++ |
| squashfs-tools/unsquash-3.c | 6 ++ |
| squashfs-tools/unsquash-4.c | 6 ++ |
| squashfs-tools/unsquashfs.h | 4 ++ |
| 8 files changed, 173 insertions(+), 2 deletions(-) |
| create mode 100644 squashfs-tools/unsquash-12.c |
| |
| diff --git a/squashfs-tools/Makefile b/squashfs-tools/Makefile |
| index 7262a2e..1b544ed 100755 |
| --- a/squashfs-tools/Makefile |
| +++ b/squashfs-tools/Makefile |
| @@ -160,8 +160,8 @@ MKSQUASHFS_OBJS = mksquashfs.o read_fs.o action.o swap.o pseudo.o compressor.o \ |
| caches-queues-lists.o reader.o tar.o |
| |
| UNSQUASHFS_OBJS = unsquashfs.o unsquash-1.o unsquash-2.o unsquash-3.o \ |
| - unsquash-4.o unsquash-123.o unsquash-34.o unsquash-1234.o swap.o \ |
| - compressor.o unsquashfs_info.o |
| + unsquash-4.o unsquash-123.o unsquash-34.o unsquash-1234.o unsquash-12.o \ |
| + swap.o compressor.o unsquashfs_info.o |
| |
| CFLAGS ?= -O2 |
| CFLAGS += $(EXTRA_CFLAGS) $(INCLUDEDIR) -D_FILE_OFFSET_BITS=64 \ |
| @@ -393,6 +393,8 @@ unsquash-34.o: unsquashfs.h unsquash-34.c unsquashfs_error.h |
| |
| unsquash-1234.o: unsquash-1234.c unsquashfs_error.h |
| |
| +unsquash-12.o: unsquash-12.c unsquashfs.h |
| + |
| unsquashfs_xattr.o: unsquashfs_xattr.c unsquashfs.h squashfs_fs.h xattr.h unsquashfs_error.h |
| |
| unsquashfs_info.o: unsquashfs.h squashfs_fs.h unsquashfs_error.h |
| diff --git a/squashfs-tools/unsquash-1.c b/squashfs-tools/unsquash-1.c |
| index b604434..88866fc 100644 |
| --- a/squashfs-tools/unsquash-1.c |
| +++ b/squashfs-tools/unsquash-1.c |
| @@ -370,6 +370,12 @@ static struct dir *squashfs_opendir(unsigned int block_start, unsigned int offse |
| } |
| } |
| |
| + /* check directory for duplicate names. Need to sort directory first */ |
| + sort_directory(dir); |
| + if(check_directory(dir) == FALSE) { |
| + ERROR("File system corrupted: directory has duplicate names\n"); |
| + goto corrupted; |
| + } |
| return dir; |
| |
| corrupted: |
| diff --git a/squashfs-tools/unsquash-12.c b/squashfs-tools/unsquash-12.c |
| new file mode 100644 |
| index 0000000..61bf128 |
| --- /dev/null |
| +++ b/squashfs-tools/unsquash-12.c |
| @@ -0,0 +1,110 @@ |
| +/* |
| + * Unsquash a squashfs filesystem. This is a highly compressed read only |
| + * filesystem. |
| + * |
| + * Copyright (c) 2021 |
| + * Phillip Lougher <phillip@squashfs.org.uk> |
| + * |
| + * This program is free software; you can redistribute it and/or |
| + * modify it under the terms of the GNU General Public License |
| + * as published by the Free Software Foundation; either version 2, |
| + * or (at your option) any later version. |
| + * |
| + * This program is distributed in the hope that it will be useful, |
| + * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| + * GNU General Public License for more details. |
| + * |
| + * You should have received a copy of the GNU General Public License |
| + * along with this program; if not, write to the Free Software |
| + * Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
| + * |
| + * unsquash-12.c |
| + * |
| + * Helper functions used by unsquash-1 and unsquash-2. |
| + */ |
| + |
| +#include "unsquashfs.h" |
| + |
| +/* |
| + * Bottom up linked list merge sort. |
| + * |
| + */ |
| +void sort_directory(struct dir *dir) |
| +{ |
| + struct dir_ent *cur, *l1, *l2, *next; |
| + int len1, len2, stride = 1; |
| + |
| + if(dir->dir_count < 2) |
| + return; |
| + |
| + /* |
| + * We can consider our linked-list to be made up of stride length |
| + * sublists. Eacn iteration around this loop merges adjacent |
| + * stride length sublists into larger 2*stride sublists. We stop |
| + * when stride becomes equal to the entire list. |
| + * |
| + * Initially stride = 1 (by definition a sublist of 1 is sorted), and |
| + * these 1 element sublists are merged into 2 element sublists, which |
| + * are then merged into 4 element sublists and so on. |
| + */ |
| + do { |
| + l2 = dir->dirs; /* head of current linked list */ |
| + cur = NULL; /* empty output list */ |
| + |
| + /* |
| + * Iterate through the linked list, merging adjacent sublists. |
| + * On each interation l2 points to the next sublist pair to be |
| + * merged (if there's only one sublist left this is simply added |
| + * to the output list) |
| + */ |
| + while(l2) { |
| + l1 = l2; |
| + for(len1 = 0; l2 && len1 < stride; len1 ++, l2 = l2->next); |
| + len2 = stride; |
| + |
| + /* |
| + * l1 points to first sublist. |
| + * l2 points to second sublist. |
| + * Merge them onto the output list |
| + */ |
| + while(len1 && l2 && len2) { |
| + if(strcmp(l1->name, l2->name) <= 0) { |
| + next = l1; |
| + l1 = l1->next; |
| + len1 --; |
| + } else { |
| + next = l2; |
| + l2 = l2->next; |
| + len2 --; |
| + } |
| + |
| + if(cur) { |
| + cur->next = next; |
| + cur = next; |
| + } else |
| + dir->dirs = cur = next; |
| + } |
| + /* |
| + * One sublist is now empty, copy the other one onto the |
| + * output list |
| + */ |
| + for(; len1; len1 --, l1 = l1->next) { |
| + if(cur) { |
| + cur->next = l1; |
| + cur = l1; |
| + } else |
| + dir->dirs = cur = l1; |
| + } |
| + for(; l2 && len2; len2 --, l2 = l2->next) { |
| + if(cur) { |
| + cur->next = l2; |
| + cur = l2; |
| + } else |
| + dir->dirs = cur = l2; |
| + } |
| + } |
| + cur->next = NULL; |
| + stride = stride << 1; |
| + } while(stride < dir->dir_count); |
| +} |
| diff --git a/squashfs-tools/unsquash-1234.c b/squashfs-tools/unsquash-1234.c |
| index e389f8d..98a81ed 100644 |
| --- a/squashfs-tools/unsquash-1234.c |
| +++ b/squashfs-tools/unsquash-1234.c |
| @@ -72,3 +72,24 @@ void squashfs_closedir(struct dir *dir) |
| |
| free(dir); |
| } |
| + |
| + |
| +/* |
| + * Check directory for duplicate names. As the directory should be sorted, |
| + * duplicates will be consecutive. Obviously we also need to check if the |
| + * directory has been deliberately unsorted, to evade this check. |
| + */ |
| +int check_directory(struct dir *dir) |
| +{ |
| + int i; |
| + struct dir_ent *ent; |
| + |
| + if(dir->dir_count < 2) |
| + return TRUE; |
| + |
| + for(ent = dir->dirs, i = 0; i < dir->dir_count - 1; ent = ent->next, i++) |
| + if(strcmp(ent->name, ent->next->name) >= 0) |
| + return FALSE; |
| + |
| + return TRUE; |
| +} |
| diff --git a/squashfs-tools/unsquash-2.c b/squashfs-tools/unsquash-2.c |
| index 956f96f..0e36f7d 100644 |
| --- a/squashfs-tools/unsquash-2.c |
| +++ b/squashfs-tools/unsquash-2.c |
| @@ -29,6 +29,7 @@ |
| static squashfs_fragment_entry_2 *fragment_table; |
| static unsigned int *uid_table, *guid_table; |
| static squashfs_operations ops; |
| +static int needs_sorting = FALSE; |
| |
| |
| static void read_block_list(unsigned int *block_list, long long start, |
| @@ -463,6 +464,17 @@ static struct dir *squashfs_opendir(unsigned int block_start, unsigned int offse |
| } |
| } |
| |
| + if(needs_sorting) |
| + sort_directory(dir); |
| + |
| + /* check directory for duplicate names and sorting */ |
| + if(check_directory(dir) == FALSE) { |
| + if(needs_sorting) |
| + ERROR("File system corrupted: directory has duplicate names\n"); |
| + else |
| + ERROR("File system corrupted: directory has duplicate names or is unsorted\n"); |
| + goto corrupted; |
| + } |
| return dir; |
| |
| corrupted: |
| @@ -596,6 +608,10 @@ int read_super_2(squashfs_operations **s_ops, void *s) |
| * 2.x filesystems use gzip compression. |
| */ |
| comp = lookup_compressor("gzip"); |
| + |
| + if(sBlk_3->s_minor == 0) |
| + needs_sorting = TRUE; |
| + |
| return TRUE; |
| } |
| |
| diff --git a/squashfs-tools/unsquash-3.c b/squashfs-tools/unsquash-3.c |
| index 835a574..0123562 100644 |
| --- a/squashfs-tools/unsquash-3.c |
| +++ b/squashfs-tools/unsquash-3.c |
| @@ -497,6 +497,12 @@ static struct dir *squashfs_opendir(unsigned int block_start, unsigned int offse |
| } |
| } |
| |
| + /* check directory for duplicate names and sorting */ |
| + if(check_directory(dir) == FALSE) { |
| + ERROR("File system corrupted: directory has duplicate names or is unsorted\n"); |
| + goto corrupted; |
| + } |
| + |
| return dir; |
| |
| corrupted: |
| diff --git a/squashfs-tools/unsquash-4.c b/squashfs-tools/unsquash-4.c |
| index 694783d..c615bb8 100644 |
| --- a/squashfs-tools/unsquash-4.c |
| +++ b/squashfs-tools/unsquash-4.c |
| @@ -434,6 +434,12 @@ static struct dir *squashfs_opendir(unsigned int block_start, unsigned int offse |
| } |
| } |
| |
| + /* check directory for duplicate names and sorting */ |
| + if(check_directory(dir) == FALSE) { |
| + ERROR("File system corrupted: directory has duplicate names or is unsorted\n"); |
| + goto corrupted; |
| + } |
| + |
| return dir; |
| |
| corrupted: |
| diff --git a/squashfs-tools/unsquashfs.h b/squashfs-tools/unsquashfs.h |
| index f8cf78c..bf2a80d 100644 |
| --- a/squashfs-tools/unsquashfs.h |
| +++ b/squashfs-tools/unsquashfs.h |
| @@ -293,4 +293,8 @@ extern long long *alloc_index_table(int); |
| /* unsquash-1234.c */ |
| extern int check_name(char *, int); |
| extern void squashfs_closedir(struct dir *); |
| +extern int check_directory(struct dir *); |
| + |
| +/* unsquash-12.c */ |
| +extern void sort_directory(struct dir *); |
| #endif |
| -- |
| 2.17.1 |
| |