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Diffstat (limited to 'fs/namei.c')
-rw-r--r--fs/namei.c53
1 files changed, 50 insertions, 3 deletions
diff --git a/fs/namei.c b/fs/namei.c
index ae6aa9ae757c..0cab6494978c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -887,6 +887,8 @@ static inline void put_link(struct nameidata *nd)
int sysctl_protected_symlinks __read_mostly = 0;
int sysctl_protected_hardlinks __read_mostly = 0;
+int sysctl_protected_fifos __read_mostly;
+int sysctl_protected_regular __read_mostly;
/**
* may_follow_link - Check symlink following for unsafe situations
@@ -1003,6 +1005,45 @@ static int may_linkat(struct path *link)
return -EPERM;
}
+/**
+ * may_create_in_sticky - Check whether an O_CREAT open in a sticky directory
+ * should be allowed, or not, on files that already
+ * exist.
+ * @dir: the sticky parent directory
+ * @inode: the inode of the file to open
+ *
+ * Block an O_CREAT open of a FIFO (or a regular file) when:
+ * - sysctl_protected_fifos (or sysctl_protected_regular) is enabled
+ * - the file already exists
+ * - we are in a sticky directory
+ * - we don't own the file
+ * - the owner of the directory doesn't own the file
+ * - the directory is world writable
+ * If the sysctl_protected_fifos (or sysctl_protected_regular) is set to 2
+ * the directory doesn't have to be world writable: being group writable will
+ * be enough.
+ *
+ * Returns 0 if the open is allowed, -ve on error.
+ */
+static int may_create_in_sticky(struct dentry * const dir,
+ struct inode * const inode)
+{
+ if ((!sysctl_protected_fifos && S_ISFIFO(inode->i_mode)) ||
+ (!sysctl_protected_regular && S_ISREG(inode->i_mode)) ||
+ likely(!(dir->d_inode->i_mode & S_ISVTX)) ||
+ uid_eq(inode->i_uid, dir->d_inode->i_uid) ||
+ uid_eq(current_fsuid(), inode->i_uid))
+ return 0;
+
+ if (likely(dir->d_inode->i_mode & 0002) ||
+ (dir->d_inode->i_mode & 0020 &&
+ ((sysctl_protected_fifos >= 2 && S_ISFIFO(inode->i_mode)) ||
+ (sysctl_protected_regular >= 2 && S_ISREG(inode->i_mode))))) {
+ return -EACCES;
+ }
+ return 0;
+}
+
static __always_inline
const char *get_link(struct nameidata *nd)
{
@@ -3348,9 +3389,15 @@ finish_open:
if (error)
return error;
audit_inode(nd->name, nd->path.dentry, 0);
- error = -EISDIR;
- if ((open_flag & O_CREAT) && d_is_dir(nd->path.dentry))
- goto out;
+ if (open_flag & O_CREAT) {
+ error = -EISDIR;
+ if (d_is_dir(nd->path.dentry))
+ goto out;
+ error = may_create_in_sticky(dir,
+ d_backing_inode(nd->path.dentry));
+ if (unlikely(error))
+ goto out;
+ }
error = -ENOTDIR;
if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry))
goto out;