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libbpf: Set MFD_NOEXEC_SEAL when creating memfd

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Starting from 105ff5339f49 ("mm/memfd: add MFD_NOEXEC_SEAL and
MFD_EXEC") and until 1717449b4417 ("memfd: drop warning for missing
exec-related flags"), the kernel would print a warning if neither
MFD_NOEXEC_SEAL nor MFD_EXEC is set in memfd_create().

If libbpf runs on on a kernel between these two commits (eg. on an
improperly backported system), it'll trigger this warning.

To avoid this warning (and also be more secure), explicitly set
MFD_NOEXEC_SEAL. But since libbpf can be run on potentially very old
kernels, leave a fallback for kernels without MFD_NOEXEC_SEAL support.

Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
Link: https://lore.kernel.org/r/6e62c2421ad7eb1da49cbf16da95aaaa7f94d394.1735594195.git.dxu@dxuuu.xyz
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Xu 2024-12-30 14:31:22 -07:00 committed by Alexei Starovoitov
parent c5d2bac978
commit 1846dd8e3a
1 changed files with 13 additions and 1 deletions
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14
tools/lib/bpf/libbpf.c
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@ -1731,12 +1731,24 @@ static int sys_memfd_create(const char *name, unsigned flags)
#ifndef MFD_CLOEXEC
#define MFD_CLOEXEC 0x0001U
#endif
#ifndef MFD_NOEXEC_SEAL
#define MFD_NOEXEC_SEAL 0x0008U
#endif
static int create_placeholder_fd(void)
{
unsigned int flags = MFD_CLOEXEC | MFD_NOEXEC_SEAL;
const char *name = "libbpf-placeholder-fd";
int fd;
fd = ensure_good_fd(sys_memfd_create("libbpf-placeholder-fd", MFD_CLOEXEC));
fd = ensure_good_fd(sys_memfd_create(name, flags));
if (fd >= 0)
return fd;
else if (errno != EINVAL)
return -errno;
/* Possibly running on kernel without MFD_NOEXEC_SEAL */
fd = ensure_good_fd(sys_memfd_create(name, flags & ~MFD_NOEXEC_SEAL));
if (fd < 0)
return -errno;
return fd;