mkfs.ubifs problem when output file really isn't in the UBIFS root directory
Marcus Prebble
marcus.prebble at axis.com
Wed Oct 10 11:26:25 EDT 2012
Hi Artem,
Big thanks for the provided patch. It seems to solve the problem we here
at Axis and other users were having.
When trying to break it (unsuccessfully) I found that if the directory
of the output file was non-existent then the function would return -1
(correct), but the error messages were:
"realpath: no such file or directory"
"Error: output file cannot be in the UBIFS root directory"
which was a tad confusing. Please find attached a new diff (based off
yours) with a few minor suggested changes.
Kind regards,
/Marcus Prebble
On Wed, 2012-10-10 at 13:30 +0200, Artem Bityutskiy wrote:
> On Wed, 2012-10-10 at 12:34 +0200, Marcus Prebble wrote:
> > I will implement and come back with a patch when I have time.
>
> I actually went ahead and cooked something. Could you please review and
> give it a test? Inlined below and also attached. Thanks!
>
>
> From 7c1b939f2cf0141dfb1969d51b4157a75f55ddac Mon Sep 17 00:00:00 2001
> From: Artem Bityutskiy <artem.bityutskiy at linux.intel.com>
> Date: Wed, 10 Oct 2012 14:23:18 +0300
> Subject: [PATCH] mkfs.ubifs: rewrite path checking
>
> We use the 'in_path()' function to check whether the output image is
> withing the mkfs.ubifs root directory or not. However, this function
> is not correct and it fails for the following situation, as
> Marcus Prebble <marcus.prebble at axis.com> reports:
>
> 1. We have our root file-system mounted at / and want to build an image
> out of it.
> 2. We have tmpfs mounted at /tmp
> 3. We mount the root file-system under /tmp/newroot
> 4. We run mkfs.ubifs with -r /tmp/newroot -o /tmp/image
>
> And this fails. It fails because 'in_path()' misses this use-case.
>
> This patch re-implements the check completely. Now we use 'realpath()'
> to find canonical paths and just check that the output file is not
> under the root mkfs.ubifs directory.
>
> Signed-off-by: Artem Bityutskiy <artem.bityutskiy at linux.intel.com>
> ---
> mkfs.ubifs/mkfs.ubifs.c | 116 +++++++++++++++---------------------------------
> 1 file changed, 37 insertions(+), 79 deletions(-)
>
> diff --git a/mkfs.ubifs/mkfs.ubifs.c b/mkfs.ubifs/mkfs.ubifs.c
> index 149806b..885c202 100644
> --- a/mkfs.ubifs/mkfs.ubifs.c
> +++ b/mkfs.ubifs/mkfs.ubifs.c
> @@ -20,6 +20,7 @@
> * Zoltan Sogor
> */
>
> +#define _XOPEN_SOURCE 500 /* For realpath() */
> #define PROGRAM_NAME "mkfs.ubifs"
>
> #include "mkfs.ubifs.h"
> @@ -235,93 +236,50 @@ static char *make_path(const char *dir, const char *name)
> }
>
> /**
> - * same_dir - determine if two file descriptors refer to the same directory.
> - * @fd1: file descriptor 1
> - * @fd2: file descriptor 2
> - */
> -static int same_dir(int fd1, int fd2)
> -{
> - struct stat stat1, stat2;
> -
> - if (fstat(fd1, &stat1) == -1)
> - return -1;
> - if (fstat(fd2, &stat2) == -1)
> - return -1;
> - return stat1.st_dev == stat2.st_dev && stat1.st_ino == stat2.st_ino;
> -}
> -
> -/**
> - * do_openat - open a file in a directory.
> - * @fd: file descriptor of open directory
> - * @path: path relative to directory
> - * @flags: open flags
> + * is_contained - determine if a file is beneath a directory.
> + * @file: file path name
> + * @dir: directory path name
> *
> - * This function is provided because the library function openat is sometimes
> - * not available.
> + * This function returns %1 if @file is accessible from the @dir directory and
> + * %0 otherwise. In case of error, returns %-1.
> */
> -static int do_openat(int fd, const char *path, int flags)
> +static int is_contained(const char *file, const char *dir)
> {
> - int ret;
> - char *cwd;
> + char *file_base, *copy, *real_file, *real_dir, *p;
>
> - cwd = getcwd(NULL, 0);
> - if (!cwd)
> + /* Make a copy of the file path because 'dirname()' can modify it */
> + copy = strdup(file);
> + if (!copy)
> return -1;
> - ret = fchdir(fd);
> - if (ret != -1)
> - ret = open(path, flags);
> - if (chdir(cwd) && !ret)
> - ret = -1;
> - free(cwd);
> - return ret;
> -}
> + file_base = dirname(copy);
>
> -/**
> - * in_path - determine if a file is beneath a directory.
> - * @dir_name: directory path name
> - * @file_name: file path name
> - */
> -static int in_path(const char *dir_name, const char *file_name)
> -{
> - char *fn = strdup(file_name);
> - char *dn;
> - int fd1, fd2, fd3, ret = -1, top_fd;
> + /* Turn the paths into the canonical form */
> + real_file = malloc(PATH_MAX);
> + if (!real_file) {
> + free(copy);
> + return -1;
> + }
>
> - if (!fn)
> + real_dir = malloc(PATH_MAX);
> + if (!real_dir) {
> + free(real_file);
> + free(copy);
> + return -1;
> + }
> + if (!realpath(file_base, real_file)) {
> + perror("realpath");
> return -1;
> - top_fd = open("/", O_RDONLY);
> - if (top_fd != -1) {
> - dn = dirname(fn);
> - fd1 = open(dir_name, O_RDONLY);
> - if (fd1 != -1) {
> - fd2 = open(dn, O_RDONLY);
> - if (fd2 != -1) {
> - while (1) {
> - int same;
> -
> - same = same_dir(fd1, fd2);
> - if (same) {
> - ret = same;
> - break;
> - }
> - if (same_dir(fd2, top_fd)) {
> - ret = 0;
> - break;
> - }
> - fd3 = do_openat(fd2, "..", O_RDONLY);
> - if (fd3 == -1)
> - break;
> - close(fd2);
> - fd2 = fd3;
> - }
> - close(fd2);
> - }
> - close(fd1);
> - }
> - close(top_fd);
> }
> - free(fn);
> - return ret;
> + if (!realpath(dir, real_dir)) {
> + perror("realpath");
> + return -1;
> + }
> +
> + p = strstr(real_file, real_dir);
> + free(real_dir);
> + free(real_file);
> + free(copy);
> + return !!p;
> }
>
> /**
> @@ -376,7 +334,7 @@ static int validate_options(void)
>
> if (!output)
> return err_msg("no output file or UBI volume specified");
> - if (root && in_path(root, output))
> + if (root && is_contained(output, root))
> return err_msg("output file cannot be in the UBIFS root "
> "directory");
> if (!is_power_of_2(c->min_io_size))
> --
> 1.7.11.4
>
>
>
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