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use new SYS_faccessat2 syscall to implement faccessat with flags

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commit 0a05eace16 implemented AT_EACCESS
for faccessat with a horrible hack, creating a child process to change
switch uid/gid and perform the access probe without making potentially
irreversible changes to the caller's credentials. this was due to the
syscall lacking a flags argument.

linux 5.8 introduced a new syscall, SYS_faccessat2, fixing this
deficiency. use it if any flags are passed, and fallback to the old
strategy on ENOSYS. continue using the old syscall when there are no
flags.
This commit is contained in:
Rich Felker 2020-09-09 21:55:11 -04:00
parent f035c7b1e6
commit 55fb9a1773
1 changed files with 8 additions and 3 deletions
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11
src/unistd/faccessat.c
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@ -25,12 +25,17 @@ static int checker(void *p)
int faccessat(int fd, const char *filename, int amode, int flag)
{
if (!flag || (flag==AT_EACCESS && getuid()==geteuid() && getgid()==getegid()))
return syscall(SYS_faccessat, fd, filename, amode, flag);
if (flag) {
int ret = __syscall(SYS_faccessat2, fd, filename, amode, flag);
if (ret != -ENOSYS) return __syscall_ret(ret);
}
if (flag != AT_EACCESS)
if (flag & ~AT_EACCESS)
return __syscall_ret(-EINVAL);
if (!flag || (getuid()==geteuid() && getgid()==getegid()))
return syscall(SYS_faccessat, fd, filename, amode);
char stack[1024];
sigset_t set;
pid_t pid;