has already been checked. The wrappers will override a EACCES result
by gaining root privileges if the 'pvfs:perm override' is set on the
share (it is enabled by default)
+
+ Careful use of O_NOFOLLOW and O_DIRECTORY is used to prevent
+ security attacks via symlinks
+ */
+
+
+struct pvfs_sys_ctx {
+ struct pvfs_state *pvfs;
+ void *privs;
+ const char *old_wd;
+ struct stat st_orig;
+};
+
+/*
+ return to original directory when context is destroyed
+ */
+static int pvfs_sys_pushdir_destructor(struct pvfs_sys_ctx *ctx)
+{
+ struct stat st;
+
+ if (ctx->old_wd == NULL) {
+ return 0;
+ }
+
+ if (chdir(ctx->old_wd) != 0) {
+ smb_panic("Failed to restore working directory");
+ }
+ if (stat(".", &st) != 0) {
+ smb_panic("Failed to stat working directory");
+ }
+ if (st.st_ino != ctx->st_orig.st_ino ||
+ st.st_dev != ctx->st_orig.st_dev) {
+ smb_panic("Working directory changed during call");
+ }
+
+ return 0;
+}
+
+
+/*
+ chdir() to the directory part of a pathname, but disallow any
+ component with a symlink
+
+ Note that we can't use O_NOFOLLOW on the whole path as that only
+ prevents links in the final component of the path
+ */
+static int pvfs_sys_chdir_nosymlink(struct pvfs_sys_ctx *ctx, const char *pathname)
+{
+ char *p, *path;
+ size_t base_len = strlen(ctx->pvfs->base_directory);
+
+ /* don't check for symlinks in the base directory of the share */
+ if (strncmp(ctx->pvfs->base_directory, pathname, base_len) == 0 &&
+ pathname[base_len] == '/') {
+ if (chdir(ctx->pvfs->base_directory) != 0) {
+ return -1;
+ }
+ pathname += base_len + 1;
+ }
+
+ path = talloc_strdup(ctx, pathname);
+ if (path == NULL) {
+ return -1;
+ }
+ while ((p = strchr(path, '/'))) {
+ int fd;
+ struct stat st1, st2;
+ *p = 0;
+ fd = open(path, O_NOFOLLOW | O_DIRECTORY | O_RDONLY);
+ if (fd == -1) {
+ return -1;
+ }
+ if (chdir(path) != 0) {
+ close(fd);
+ return -1;
+ }
+ if (stat(".", &st1) != 0 ||
+ fstat(fd, &st2) != 0) {
+ close(fd);
+ return -1;
+ }
+ close(fd);
+ if (st1.st_ino != st2.st_ino ||
+ st1.st_dev != st2.st_dev) {
+ DEBUG(0,(__location__ ": Inode changed during chdir in '%s' - symlink attack?",
+ pathname));
+ return -1;
+ }
+ path = p + 1;
+ }
+
+ return 0;
+}
+
+
+/*
+ become root, and change directory to the directory component of a
+ path. Return a talloc context which when freed will move us back
+ to the original directory, and return us to the original uid
+
+ change the pathname argument to contain just the base component of
+ the path
+
+ return NULL on error, which could include an attempt to subvert
+ security using symlink tricks
*/
+static struct pvfs_sys_ctx *pvfs_sys_pushdir(struct pvfs_state *pvfs,
+ const char **pathname)
+{
+ struct pvfs_sys_ctx *ctx;
+ char *cwd, *p, *dirname;
+ int ret;
+
+ ctx = talloc_zero(pvfs, struct pvfs_sys_ctx);
+ if (ctx == NULL) {
+ return NULL;
+ }
+ ctx->pvfs = pvfs;
+ ctx->privs = root_privileges();
+ if (ctx->privs == NULL) {
+ talloc_free(ctx);
+ return NULL;
+ }
+
+ talloc_steal(ctx, ctx->privs);
+
+ if (!pathname) {
+ /* no pathname needed */
+ return ctx;
+ }
+
+ p = strrchr(*pathname, '/');
+ if (p == NULL) {
+ /* we don't need to change directory */
+ return ctx;
+ }
+
+ /* we keep the old st around, so we can tell that
+ we have come back to the right directory */
+ if (stat(".", &ctx->st_orig) != 0) {
+ talloc_free(ctx);
+ return NULL;
+ }
+
+ cwd = get_current_dir_name();
+ if (cwd == NULL) {
+ talloc_free(ctx);
+ return NULL;
+ }
+ ctx->old_wd = talloc_strdup(ctx, cwd);
+ if (ctx->old_wd == NULL) {
+ free(cwd);
+ talloc_free(ctx);
+ return NULL;
+ }
+
+ dirname = talloc_strndup(ctx, *pathname, (p - *pathname));
+ if (dirname == NULL) {
+ talloc_free(ctx);
+ return NULL;
+ }
+
+ ret = pvfs_sys_chdir_nosymlink(ctx, *pathname);
+ if (ret == -1) {
+ talloc_free(ctx);
+ return NULL;
+ }
+
+ talloc_set_destructor(ctx, pvfs_sys_pushdir_destructor);
+
+ /* return the basename as the filename that should be operated on */
+ (*pathname) = talloc_strdup(ctx, p+1);
+ if (! *pathname) {
+ talloc_free(ctx);
+ return NULL;
+ }
+
+ return ctx;
+}
/*
chown a file that we created with a root privileges override
*/
-static int pvfs_sys_fchown(struct pvfs_state *pvfs, void *privs, int fd)
+static int pvfs_sys_fchown(struct pvfs_state *pvfs, struct pvfs_sys_ctx *ctx, int fd)
{
- return fchown(fd, root_privileges_original_uid(privs), -1);
+ return fchown(fd, root_privileges_original_uid(ctx->privs), -1);
}
/*
chown a directory that we created with a root privileges override
*/
-static int pvfs_sys_chown(struct pvfs_state *pvfs, void *privs, const char *name)
+static int pvfs_sys_chown(struct pvfs_state *pvfs, struct pvfs_sys_ctx *ctx, const char *name)
{
- return chown(name, root_privileges_original_uid(privs), -1);
+ /* to avoid symlink hacks, we need to use fchown() on a directory fd */
+ int ret, fd;
+ fd = open(name, O_DIRECTORY | O_NOFOLLOW | O_RDONLY);
+ if (fd == -1) {
+ return -1;
+ }
+ ret = pvfs_sys_fchown(pvfs, ctx, fd);
+ close(fd);
+ return ret;
}
int pvfs_sys_open(struct pvfs_state *pvfs, const char *filename, int flags, mode_t mode)
{
int fd, ret;
- void *privs;
+ struct pvfs_sys_ctx *ctx;
int saved_errno, orig_errno;
int retries = 5;
}
saved_errno = errno;
- privs = root_privileges();
+ ctx = pvfs_sys_pushdir(pvfs, &filename);
+ if (ctx == NULL) {
+ errno = saved_errno;
+ return -1;
+ }
/* don't allow permission overrides to follow links */
-#ifdef O_NOFOLLOW
flags |= O_NOFOLLOW;
-#endif
/*
if O_CREAT was specified and O_EXCL was not specified
with anything other than ENOENT, then we return the
open result, with the original errno */
if (fd == -1 && errno != ENOENT) {
- talloc_free(privs);
+ talloc_free(ctx);
errno = saved_errno;
return -1;
}
if (fd != -1) {
/* the file already existed and we opened it */
- talloc_free(privs);
+ talloc_free(ctx);
errno = orig_errno;
return fd;
}
fd = open(filename, flags | O_EXCL, mode);
if (fd == -1 && errno != EEXIST) {
- talloc_free(privs);
+ talloc_free(ctx);
errno = saved_errno;
return -1;
}
if (fd != -1) {
/* we created the file, we need to set the
right ownership on it */
- ret = pvfs_sys_fchown(pvfs, privs, fd);
+ ret = pvfs_sys_fchown(pvfs, ctx, fd);
if (ret == -1) {
close(fd);
unlink(filename);
- talloc_free(privs);
+ talloc_free(ctx);
errno = saved_errno;
return -1;
}
- talloc_free(privs);
+ talloc_free(ctx);
errno = orig_errno;
return fd;
}
goto try_again;
}
- talloc_free(privs);
+ talloc_free(ctx);
errno = saved_errno;
return -1;
}
fd = open(filename, flags, mode);
if (fd == -1) {
- talloc_free(privs);
+ talloc_free(ctx);
errno = saved_errno;
return -1;
}
/* if we have created a file then fchown it */
if (flags & O_CREAT) {
- ret = pvfs_sys_fchown(pvfs, privs, fd);
+ ret = pvfs_sys_fchown(pvfs, ctx, fd);
if (ret == -1) {
close(fd);
unlink(filename);
- talloc_free(privs);
+ talloc_free(ctx);
errno = saved_errno;
return -1;
}
}
- talloc_free(privs);
+ talloc_free(ctx);
return fd;
}
int pvfs_sys_unlink(struct pvfs_state *pvfs, const char *filename)
{
int ret;
- void *privs;
+ struct pvfs_sys_ctx *ctx;
int saved_errno, orig_errno;
orig_errno = errno;
saved_errno = errno;
- privs = root_privileges();
+ ctx = pvfs_sys_pushdir(pvfs, &filename);
+ if (ctx == NULL) {
+ errno = saved_errno;
+ return -1;
+ }
+
ret = unlink(filename);
if (ret == -1) {
errno = saved_errno;
- talloc_free(privs);
+ talloc_free(ctx);
return -1;
}
errno = orig_errno;
- talloc_free(privs);
+ talloc_free(ctx);
return ret;
}
+static bool contains_symlink(const char *path)
+{
+ int fd = open(path, O_NOFOLLOW | O_RDONLY);
+ if (fd != -1) {
+ close(fd);
+ return false;
+ }
+ return (errno == ELOOP);
+}
+
/*
wrap rename for system override
*/
int pvfs_sys_rename(struct pvfs_state *pvfs, const char *name1, const char *name2)
{
int ret;
- void *privs;
+ struct pvfs_sys_ctx *ctx;
int saved_errno, orig_errno;
orig_errno = errno;
saved_errno = errno;
- privs = root_privileges();
+ ctx = pvfs_sys_pushdir(pvfs, &name1);
+ if (ctx == NULL) {
+ errno = saved_errno;
+ return -1;
+ }
+
+ /* we need the destination as an absolute path */
+ if (name2[0] != '/') {
+ name2 = talloc_asprintf(ctx, "%s/%s", ctx->old_wd, name2);
+ if (name2 == NULL) {
+ errno = saved_errno;
+ talloc_free(ctx);
+ return -1;
+ }
+ }
+
+ /* make sure the destination isn't a symlink beforehand */
+ if (contains_symlink(name2)) {
+ errno = saved_errno;
+ talloc_free(ctx);
+ return -1;
+ }
+
ret = rename(name1, name2);
if (ret == -1) {
errno = saved_errno;
- talloc_free(privs);
+ talloc_free(ctx);
+ return -1;
+ }
+
+ /* make sure the destination isn't a symlink afterwards */
+ if (contains_symlink(name2)) {
+ DEBUG(0,(__location__ ": Possible symlink attack in rename to '%s' - unlinking\n", name2));
+ unlink(name2);
+ errno = saved_errno;
+ talloc_free(ctx);
return -1;
}
errno = orig_errno;
- talloc_free(privs);
+ talloc_free(ctx);
return ret;
}
int pvfs_sys_mkdir(struct pvfs_state *pvfs, const char *dirname, mode_t mode)
{
int ret;
- void *privs;
+ struct pvfs_sys_ctx *ctx;
int saved_errno, orig_errno;
orig_errno = errno;
}
saved_errno = errno;
- privs = root_privileges();
+ ctx = pvfs_sys_pushdir(pvfs, &dirname);
+ if (ctx == NULL) {
+ errno = saved_errno;
+ return -1;
+ }
ret = mkdir(dirname, mode);
if (ret == -1) {
- talloc_free(privs);
+ talloc_free(ctx);
errno = saved_errno;
return -1;
}
- ret = pvfs_sys_chown(pvfs, privs, dirname);
+ ret = pvfs_sys_chown(pvfs, ctx, dirname);
if (ret == -1) {
rmdir(dirname);
- talloc_free(privs);
+ talloc_free(ctx);
errno = saved_errno;
return -1;
}
- talloc_free(privs);
+ talloc_free(ctx);
return ret;
}
int pvfs_sys_rmdir(struct pvfs_state *pvfs, const char *dirname)
{
int ret;
- void *privs;
+ struct pvfs_sys_ctx *ctx;
int saved_errno, orig_errno;
orig_errno = errno;
saved_errno = errno;
- privs = root_privileges();
+ ctx = pvfs_sys_pushdir(pvfs, &dirname);
+ if (ctx == NULL) {
+ errno = saved_errno;
+ return -1;
+ }
+
ret = rmdir(dirname);
if (ret == -1) {
errno = saved_errno;
- talloc_free(privs);
+ talloc_free(ctx);
+ return -1;
+ }
+
+ errno = orig_errno;
+ talloc_free(ctx);
+ return ret;
+}
+
+/*
+ wrap fchmod for system override
+*/
+int pvfs_sys_fchmod(struct pvfs_state *pvfs, int fd, mode_t mode)
+{
+ int ret;
+ struct pvfs_sys_ctx *ctx;
+ int saved_errno, orig_errno;
+
+ orig_errno = errno;
+
+ ret = fchmod(fd, mode);
+ if (ret != -1 ||
+ !(pvfs->flags & PVFS_FLAG_PERM_OVERRIDE) ||
+ errno != EACCES) {
+ return ret;
+ }
+
+ saved_errno = errno;
+
+ ctx = pvfs_sys_pushdir(pvfs, NULL);
+ if (ctx == NULL) {
+ errno = saved_errno;
+ return -1;
+ }
+
+ ret = fchmod(fd, mode);
+ if (ret == -1) {
+ errno = saved_errno;
+ talloc_free(ctx);
+ return -1;
+ }
+
+ errno = orig_errno;
+ talloc_free(ctx);
+ return ret;
+}
+
+
+/*
+ wrap chmod for system override
+*/
+int pvfs_sys_chmod(struct pvfs_state *pvfs, const char *filename, mode_t mode)
+{
+ int ret;
+ struct pvfs_sys_ctx *ctx;
+ int saved_errno, orig_errno;
+
+ orig_errno = errno;
+
+ ret = chmod(filename, mode);
+ if (ret != -1 ||
+ !(pvfs->flags & PVFS_FLAG_PERM_OVERRIDE) ||
+ errno != EACCES) {
+ return ret;
+ }
+
+ saved_errno = errno;
+
+ ctx = pvfs_sys_pushdir(pvfs, &filename);
+ if (ctx == NULL) {
+ errno = saved_errno;
+ return -1;
+ }
+
+ ret = chmod(filename, mode);
+ if (ret == -1) {
+ errno = saved_errno;
+ talloc_free(ctx);
return -1;
}
errno = orig_errno;
- talloc_free(privs);
+ talloc_free(ctx);
return ret;
}
git.samba.org / kai / samba.git / commitdiff