From: Omar Sandoval <osandov@xxxxxx>
The upcoming RWF_ENCODED operation introduces some security concerns:
1. Compressed writes will pass arbitrary data to decompression
algorithms in the kernel.
2. Compressed reads can leak truncated/hole punched data.
Therefore, we need to require privilege for RWF_ENCODED. It's not
possible to do the permissions checks at the time of the read or write
because, e.g., io_uring submits IO from a worker thread. So, add an open
flag which requires CAP_SYS_ADMIN. It can also be set and cleared with
fcntl(). The flag is not cleared in any way on fork or exec; it should
probably be used with O_CLOEXEC in most cases.
Note that the usual issue that unknown open flags are ignored doesn't
really matter for O_ENCODED; if the kernel doesn't support O_ENCODED,
then it doesn't support RWF_ENCODED, either.
Signed-off-by: Omar Sandoval <osandov@xxxxxx>
---
fs/fcntl.c | 10 ++++++++--
fs/namei.c | 4 ++++
include/linux/fcntl.h | 2 +-
include/uapi/asm-generic/fcntl.h | 4 ++++
4 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 3d40771e8e7c..45ebc6df078e 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -30,7 +30,8 @@
#include <asm/siginfo.h>
#include <linux/uaccess.h>
-#define SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT | O_NOATIME)
+#define SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT | O_NOATIME | \
+ O_ENCODED)
static int setfl(int fd, struct file * filp, unsigned long arg)
{
@@ -49,6 +50,11 @@ static int setfl(int fd, struct file * filp, unsigned long arg)
if (!inode_owner_or_capable(inode))
return -EPERM;
+ /* O_ENCODED can only be set by superuser */
+ if ((arg & O_ENCODED) && !(filp->f_flags & O_ENCODED) &&
+ !capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
/* required for strict SunOS emulation */
if (O_NONBLOCK != O_NDELAY)
if (arg & O_NDELAY)
@@ -1031,7 +1037,7 @@ static int __init fcntl_init(void)
* Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY
* is defined as O_NONBLOCK on some platforms and not on others.
*/
- BUILD_BUG_ON(21 - 1 /* for O_RDONLY being 0 */ !=
+ BUILD_BUG_ON(22 - 1 /* for O_RDONLY being 0 */ !=
HWEIGHT32(
(VALID_OPEN_FLAGS & ~(O_NONBLOCK | O_NDELAY)) |
__FMODE_EXEC | __FMODE_NONOTIFY));
diff --git a/fs/namei.c b/fs/namei.c
index 671c3c1a3425..ae86b125888a 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2978,6 +2978,10 @@ static int may_open(const struct path *path, int acc_mode, int flag)
if (flag & O_NOATIME && !inode_owner_or_capable(inode))
return -EPERM;
+ /* O_ENCODED can only be set by superuser */
+ if ((flag & O_ENCODED) && !capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
return 0;
}
diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h
index d019df946cb2..5fac02479639 100644
--- a/include/linux/fcntl.h
+++ b/include/linux/fcntl.h
@@ -9,7 +9,7 @@
(O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | \
O_APPEND | O_NDELAY | O_NONBLOCK | O_NDELAY | __O_SYNC | O_DSYNC | \
FASYNC | O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \
- O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE)
+ O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE | O_ENCODED)
#ifndef force_o_largefile
#define force_o_largefile() (!IS_ENABLED(CONFIG_ARCH_32BIT_OFF_T))
diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
index 9dc0bf0c5a6e..8c5cbd5942e3 100644
--- a/include/uapi/asm-generic/fcntl.h
+++ b/include/uapi/asm-generic/fcntl.h
@@ -97,6 +97,10 @@
#define O_NDELAY O_NONBLOCK
#endif
+#ifndef O_ENCODED
+#define O_ENCODED 040000000
+#endif
+
#define F_DUPFD 0 /* dup */
#define F_GETFD 1 /* get close_on_exec */
#define F_SETFD 2 /* set/clear close_on_exec */
--
2.23.0
