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authorMiklos Szeredi <miklos@szeredi.hu>2005-09-09 13:10:34 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2005-09-09 14:03:46 -0700
commit87729a5514e855ce2c71e3e33833a106b8caf2ae (patch)
treedd2e7a9fd96b2dd3ebc3951fef2d682e83aa6bb4
parentdb50b96c0f28a21c5a4a19ecaba12d0972aab06a (diff)
downloadlinux-stericsson-87729a5514e855ce2c71e3e33833a106b8caf2ae.tar.gz
[PATCH] FUSE: tighten check for processes allowed access
This patch tightens the check for allowing processes to access non-privileged mounts. The rational is that the filesystem implementation can control the behavior or get otherwise unavailable information of the filesystem user. If the filesystem user process has the same uid, gid, and is not suid or sgid application, then access is safe. Otherwise access is not allowed unless the "allow_other" mount option is given (for which policy is controlled by the userspace mount utility). Thanks to everyone linux-fsdevel, especially Martin Mares who helped uncover problems with the previous approach. Signed-off-by: Miklos Szeredi <miklos@szeredi.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--fs/fuse/dir.c40
-rw-r--r--fs/fuse/fuse_i.h3
-rw-r--r--fs/fuse/inode.c12
3 files changed, 49 insertions, 6 deletions
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index f127625543b4..65da6e1b6de5 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -411,17 +411,45 @@ int fuse_do_getattr(struct inode *inode)
return err;
}
+/*
+ * Calling into a user-controlled filesystem gives the filesystem
+ * daemon ptrace-like capabilities over the requester process. This
+ * means, that the filesystem daemon is able to record the exact
+ * filesystem operations performed, and can also control the behavior
+ * of the requester process in otherwise impossible ways. For example
+ * it can delay the operation for arbitrary length of time allowing
+ * DoS against the requester.
+ *
+ * For this reason only those processes can call into the filesystem,
+ * for which the owner of the mount has ptrace privilege. This
+ * excludes processes started by other users, suid or sgid processes.
+ */
+static int fuse_allow_task(struct fuse_conn *fc, struct task_struct *task)
+{
+ if (fc->flags & FUSE_ALLOW_OTHER)
+ return 1;
+
+ if (task->euid == fc->user_id &&
+ task->suid == fc->user_id &&
+ task->uid == fc->user_id &&
+ task->egid == fc->group_id &&
+ task->sgid == fc->group_id &&
+ task->gid == fc->group_id)
+ return 1;
+
+ return 0;
+}
+
static int fuse_revalidate(struct dentry *entry)
{
struct inode *inode = entry->d_inode;
struct fuse_inode *fi = get_fuse_inode(inode);
struct fuse_conn *fc = get_fuse_conn(inode);
- if (get_node_id(inode) == FUSE_ROOT_ID) {
- if (!(fc->flags & FUSE_ALLOW_OTHER) &&
- current->fsuid != fc->user_id)
- return -EACCES;
- } else if (time_before_eq(jiffies, fi->i_time))
+ if (!fuse_allow_task(fc, current))
+ return -EACCES;
+ if (get_node_id(inode) != FUSE_ROOT_ID &&
+ time_before_eq(jiffies, fi->i_time))
return 0;
return fuse_do_getattr(inode);
@@ -431,7 +459,7 @@ static int fuse_permission(struct inode *inode, int mask, struct nameidata *nd)
{
struct fuse_conn *fc = get_fuse_conn(inode);
- if (!(fc->flags & FUSE_ALLOW_OTHER) && current->fsuid != fc->user_id)
+ if (!fuse_allow_task(fc, current))
return -EACCES;
else if (fc->flags & FUSE_DEFAULT_PERMISSIONS) {
int err = generic_permission(inode, mask, NULL);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index aff3a01ea02b..3ec2aff3fdb5 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -198,6 +198,9 @@ struct fuse_conn {
/** The user id for this mount */
uid_t user_id;
+ /** The group id for this mount */
+ gid_t group_id;
+
/** The fuse mount flags for this mount */
unsigned flags;
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 0b75c73386e9..c8e54c0658f1 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -31,6 +31,7 @@ struct fuse_mount_data {
int fd;
unsigned rootmode;
unsigned user_id;
+ unsigned group_id;
unsigned flags;
unsigned max_read;
};
@@ -199,6 +200,7 @@ static void fuse_put_super(struct super_block *sb)
spin_lock(&fuse_lock);
fc->mounted = 0;
fc->user_id = 0;
+ fc->group_id = 0;
fc->flags = 0;
/* Flush all readers on this fs */
wake_up_all(&fc->waitq);
@@ -248,6 +250,7 @@ enum {
OPT_FD,
OPT_ROOTMODE,
OPT_USER_ID,
+ OPT_GROUP_ID,
OPT_DEFAULT_PERMISSIONS,
OPT_ALLOW_OTHER,
OPT_KERNEL_CACHE,
@@ -259,6 +262,7 @@ static match_table_t tokens = {
{OPT_FD, "fd=%u"},
{OPT_ROOTMODE, "rootmode=%o"},
{OPT_USER_ID, "user_id=%u"},
+ {OPT_GROUP_ID, "group_id=%u"},
{OPT_DEFAULT_PERMISSIONS, "default_permissions"},
{OPT_ALLOW_OTHER, "allow_other"},
{OPT_KERNEL_CACHE, "kernel_cache"},
@@ -300,6 +304,12 @@ static int parse_fuse_opt(char *opt, struct fuse_mount_data *d)
d->user_id = value;
break;
+ case OPT_GROUP_ID:
+ if (match_int(&args[0], &value))
+ return 0;
+ d->group_id = value;
+ break;
+
case OPT_DEFAULT_PERMISSIONS:
d->flags |= FUSE_DEFAULT_PERMISSIONS;
break;
@@ -333,6 +343,7 @@ static int fuse_show_options(struct seq_file *m, struct vfsmount *mnt)
struct fuse_conn *fc = get_fuse_conn_super(mnt->mnt_sb);
seq_printf(m, ",user_id=%u", fc->user_id);
+ seq_printf(m, ",group_id=%u", fc->group_id);
if (fc->flags & FUSE_DEFAULT_PERMISSIONS)
seq_puts(m, ",default_permissions");
if (fc->flags & FUSE_ALLOW_OTHER)
@@ -465,6 +476,7 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
fc->flags = d.flags;
fc->user_id = d.user_id;
+ fc->group_id = d.group_id;
fc->max_read = d.max_read;
if (fc->max_read / PAGE_CACHE_SIZE < fc->bdi.ra_pages)
fc->bdi.ra_pages = fc->max_read / PAGE_CACHE_SIZE;