POSIX defines faccessat() as having a fourth "flags" argument, while the linux syscall doesn't have it. Glibc tries to emulate AT_EACCESS and AT_SYMLINK_NOFOLLOW, but AT_EACCESS emulation is broken. Add a new faccessat(2) syscall with the added flags argument and implement both flags. The value of AT_EACCESS is defined in glibc headers to be the same as AT_REMOVEDIR. Use this value for the kernel interface as well, together with the explanatory comment. Also add AT_EMPTY_PATH support, which is not documented by POSIX, but can be useful and is trivial to implement.
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| @@ -84,10 +84,20 @@ · 83 unmodified lines | ||
| 84 | 84 | #define DN_ATTRIB 0x00000020 /* File changed attibutes */ |
| 85 | 85 | #define DN_MULTISHOT 0x80000000 /* Don't remove notifier */ |
| 86 | 86 | |
| 87 | +/* | |
| 88 | + * The constants AT_REMOVEDIR and AT_EACCESS have the same value. AT_EACCESS is | |
| 89 | + * meaningful only to faccessat, while AT_REMOVEDIR is meaningful only to | |
| 90 | + * unlinkat. The two functions do completely different things and therefore, | |
| 91 | + * the flags can be allowed to overlap. For example, passing AT_REMOVEDIR to | |
| 92 | + * faccessat would be undefined behavior and thus treating it equivalent to | |
| 93 | + * AT_EACCESS is valid undefined behavior. | |
| 94 | + */ | |
| 87 | 95 | #define AT_FDCWD -100 /* Special value used to indicate |
| 88 | 96 | openat should use the current |
| 89 | 97 | working directory. */ |
| 90 | 98 | #define AT_SYMLINK_NOFOLLOW 0x100 /* Do not follow symbolic links. */ |
| 99 | +#define AT_EACCESS 0x200 /* Test access permitted for | |
| 100 | + effective IDs, not real IDs. */ | |
| 91 | 101 | #define AT_REMOVEDIR 0x200 /* Remove directory instead of |
| 92 | 102 | unlinking file. */ |
| 93 | 103 | #define AT_SYMLINK_FOLLOW 0x400 /* Follow symbolic links. */ |