[PATCH v4 2/9] fs: add O_ALLOW_ENCODED open flag
From: Omar Sandoval <osandov@osandov.com>
Date: 2020-02-28 23:14:23
Also in:
linux-btrfs, linux-fsdevel
Subsystem:
alpha port, file locking (flock() and fcntl()/lockf()), filesystems (vfs and infrastructure), generic include/asm header files, parisc architecture, sparc + ultrasparc (sparc/sparc64), the rest · Maintainers:
Richard Henderson, Matt Turner, Magnus Lindholm, Jeff Layton, Chuck Lever, Alexander Viro, Christian Brauner, Arnd Bergmann, "James E.J. Bottomley", Helge Deller, "David S. Miller", Andreas Larsson, Linus Torvalds
From: Omar Sandoval <redacted> 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_ALLOW_ENCODED; if the kernel doesn't support O_ALLOW_ENCODED, then it doesn't support RWF_ENCODED, either. Signed-off-by: Omar Sandoval <redacted> --- arch/alpha/include/uapi/asm/fcntl.h | 1 + arch/parisc/include/uapi/asm/fcntl.h | 1 + arch/sparc/include/uapi/asm/fcntl.h | 1 + fs/fcntl.c | 10 ++++++++-- fs/namei.c | 4 ++++ include/linux/fcntl.h | 2 +- include/uapi/asm-generic/fcntl.h | 4 ++++ 7 files changed, 20 insertions(+), 3 deletions(-)
diff --git a/arch/alpha/include/uapi/asm/fcntl.h b/arch/alpha/include/uapi/asm/fcntl.h
index 50bdc8e8a271..391e0d112e41 100644
--- a/arch/alpha/include/uapi/asm/fcntl.h
+++ b/arch/alpha/include/uapi/asm/fcntl.h@@ -34,6 +34,7 @@ #define O_PATH 040000000 #define __O_TMPFILE 0100000000 +#define O_ALLOW_ENCODED 0200000000 #define F_GETLK 7 #define F_SETLK 8
diff --git a/arch/parisc/include/uapi/asm/fcntl.h b/arch/parisc/include/uapi/asm/fcntl.h
index 03ce20e5ad7d..1188b27002b3 100644
--- a/arch/parisc/include/uapi/asm/fcntl.h
+++ b/arch/parisc/include/uapi/asm/fcntl.h@@ -22,6 +22,7 @@ #define O_PATH 020000000 #define __O_TMPFILE 040000000 +#define O_ALLOW_ENCODED 100000000 #define F_GETLK64 8 #define F_SETLK64 9
diff --git a/arch/sparc/include/uapi/asm/fcntl.h b/arch/sparc/include/uapi/asm/fcntl.h
index 67dae75e5274..ac3e8c9cb32c 100644
--- a/arch/sparc/include/uapi/asm/fcntl.h
+++ b/arch/sparc/include/uapi/asm/fcntl.h@@ -37,6 +37,7 @@ #define O_PATH 0x1000000 #define __O_TMPFILE 0x2000000 +#define O_ALLOW_ENCODED 0x8000000 #define F_GETOWN 5 /* for sockets. */ #define F_SETOWN 6 /* for sockets. */
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 9bc167562ee8..c5e169115e55 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_ALLOW_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_ALLOW_ENCODED can only be set by superuser */ + if ((arg & O_ALLOW_ENCODED) && !(filp->f_flags & O_ALLOW_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 db6565c99825..4546de90281a 100644
--- a/fs/namei.c
+++ b/fs/namei.c@@ -3063,6 +3063,10 @@ 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_ALLOW_ENCODED can only be set by superuser */ + if ((flag & O_ALLOW_ENCODED) && !capable(CAP_SYS_ADMIN)) + return -EPERM; + return 0; }
diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h
index 7bcdcf4f6ab2..670939ea3c80 100644
--- a/include/linux/fcntl.h
+++ b/include/linux/fcntl.h@@ -10,7 +10,7 @@ (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_ALLOW_ENCODED) /* List of all valid flags for the how->upgrade_mask argument: */ #define VALID_UPGRADE_FLAGS \
diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
index 9dc0bf0c5a6e..75321c7a66ac 100644
--- a/include/uapi/asm-generic/fcntl.h
+++ b/include/uapi/asm-generic/fcntl.h@@ -89,6 +89,10 @@ #define __O_TMPFILE 020000000 #endif +#ifndef O_ALLOW_ENCODED +#define O_ALLOW_ENCODED 040000000 +#endif + /* a horrid kludge trying to make sure that this will fail on old kernels */ #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY) #define O_TMPFILE_MASK (__O_TMPFILE | O_DIRECTORY | O_CREAT)
--
2.25.1