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shared: memfd_create: try MFD_NOEXEC_SEAL

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Effective from Linux 6.3 onward, this creates the memfd without execute
permissions and prevents that setting from ever being changed. A
run-time fallback is made to not using MFD_NOEXEC_SEAL when
weston compiled on Linux >= 6.3 is run on Linux < 6.3.

Signed-off-by: Sami Uddin <sami.uddin@astc-design.com>
This commit is contained in:
Sami Uddin 2024-05-15 15:22:19 +09:30
parent 27bf066c81
commit bedd171d5d
1 changed files with 20 additions and 1 deletions
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21
shared/os-compatibility.c
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@ -40,6 +40,11 @@
#define READONLY_SEALS (F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_WRITE)
/* Fallback to no flag when missing the definition */
#ifndef MFD_NOEXEC_SEAL
#define MFD_NOEXEC_SEAL 0
#endif
int
os_fd_clear_cloexec(int fd)
{
@ -184,7 +189,21 @@ os_create_anonymous_file(off_t size)
int ret;
#ifdef HAVE_MEMFD_CREATE
fd = memfd_create("weston-shared", MFD_CLOEXEC | MFD_ALLOW_SEALING);
/*
* Linux kernels older than 6.3 reject MFD_NOEXEC_SEAL with EINVAL.
* Try first *with* it, and if that fails, try again *without* it.
*/
errno = 0;
fd = memfd_create(
"weston-shared",
MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_NOEXEC_SEAL);
if (fd < 0 && errno == EINVAL && MFD_NOEXEC_SEAL != 0) {
fd = memfd_create(
"weston-shared",
MFD_CLOEXEC | MFD_ALLOW_SEALING);
}
if (fd >= 0) {
/* We can add this seal before calling posix_fallocate(), as
* the file is currently zero-sized anyway.