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Merge pull request #27005 from poettering/fd-reopen-symlink

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fd_reopen() symlink handling tweaks
This commit is contained in:
Daan De Meyer
2023-03-27 19:32:05 +02:00
committed by GitHub
parent 16d6acd08b 09a7cef5ab
commit ffa859388b
2 changed files with 40 additions and 9 deletions
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src/basic/fd-util.c
+14 -1
View File
@@ -753,7 +753,20 @@ int fd_reopen(int fd, int flags) {
*
* This implicitly resets the file read index to 0.
*
* If AT_FDCWD is specified as file descriptor gets an fd to the current cwd */
* If AT_FDCWD is specified as file descriptor gets an fd to the current cwd.
*
* If the specified file descriptor refers to a symlink via O_PATH, then this function cannot be used
* to follow that symlink. Because we cannot have non-O_PATH fds to symlinks reopening it without
* O_PATH will always result in -ELOOP. Or in other words: if you have an O_PATH fd to a symlink you
* can reopen it only if you pass O_PATH again. */
if (FLAGS_SET(flags, O_NOFOLLOW))
/* O_NOFOLLOW is not allowed in fd_reopen(), because after all this is primarily implemented
* via a symlink-based interface in /proc/self/fd. Let's refuse this here early. Note that
* the kernel would generate ELOOP here too, hence this manual check is mostly redundant –
* the only reason we add it here is so that the O_DIRECTORY special case (see below) behaves
* the same way as the non-O_DIRECTORY case. */
return -ELOOP;
if (FLAGS_SET(flags, O_DIRECTORY) || fd == AT_FDCWD) {
/* If we shall reopen the fd as directory we can just go via "." and thus bypass the whole
src/test/test-fd-util.c
+26 -8
View File
@@ -22,6 +22,7 @@
#include "rm-rf.h"
#include "seccomp-util.h"
#include "serialize.h"
#include "stat-util.h"
#include "string-util.h"
#include "tests.h"
#include "tmpfile-util.h"
@@ -410,13 +411,16 @@ TEST(fd_reopen) {
assert_se(FLAGS_SET(fl, O_DIRECTORY));
assert_se(FLAGS_SET(fl, O_PATH));
/* fd_reopen() with O_NOFOLLOW will systematically fail, since it is implemented via a symlink in /proc/self/fd/ */
assert_se(fd_reopen(fd1, O_RDONLY|O_CLOEXEC|O_NOFOLLOW) == -ELOOP);
assert_se(fd_reopen(fd1, O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOFOLLOW) == -ELOOP);
fd2 = fd_reopen(fd1, O_RDONLY|O_DIRECTORY|O_CLOEXEC); /* drop the O_PATH */
assert_se(fd2 >= 0);
assert_se(fstat(fd2, &st2) >= 0);
assert_se(S_ISDIR(st2.st_mode));
assert_se(st1.st_ino == st2.st_ino);
assert_se(st1.st_rdev == st2.st_rdev);
assert_se(stat_inode_same(&st1, &st2));
fl = fcntl(fd2, F_GETFL);
assert_se(fl >= 0);
@@ -430,8 +434,7 @@ TEST(fd_reopen) {
assert_se(fstat(fd1, &st1) >= 0);
assert_se(S_ISDIR(st1.st_mode));
assert_se(st1.st_ino == st2.st_ino);
assert_se(st1.st_rdev == st2.st_rdev);
assert_se(stat_inode_same(&st1, &st2));
fl = fcntl(fd1, F_GETFL);
assert_se(fl >= 0);
@@ -458,8 +461,7 @@ TEST(fd_reopen) {
assert_se(fstat(fd2, &st2) >= 0);
assert_se(S_ISREG(st2.st_mode));
assert_se(st1.st_ino == st2.st_ino);
assert_se(st1.st_rdev == st2.st_rdev);
assert_se(stat_inode_same(&st1, &st2));
fl = fcntl(fd2, F_GETFL);
assert_se(fl >= 0);
@@ -474,8 +476,7 @@ TEST(fd_reopen) {
assert_se(fstat(fd1, &st1) >= 0);
assert_se(S_ISREG(st1.st_mode));
assert_se(st1.st_ino == st2.st_ino);
assert_se(st1.st_rdev == st2.st_rdev);
assert_se(stat_inode_same(&st1, &st2));
fl = fcntl(fd1, F_GETFL);
assert_se(fl >= 0);
@@ -486,6 +487,23 @@ TEST(fd_reopen) {
safe_close(fd1);
assert_se(fd_reopen(fd1, O_RDONLY|O_CLOEXEC) == -EBADF);
fd1 = -EBADF;
/* Validate what happens if we reopen a symlink */
fd1 = open("/proc/self", O_PATH|O_CLOEXEC|O_NOFOLLOW);
assert_se(fd1 >= 0);
assert_se(fstat(fd1, &st1) >= 0);
assert_se(S_ISLNK(st1.st_mode));
fd2 = fd_reopen(fd1, O_PATH|O_CLOEXEC);
assert_se(fd2 >= 0);
assert_se(fstat(fd2, &st2) >= 0);
assert_se(S_ISLNK(st2.st_mode));
assert_se(stat_inode_same(&st1, &st2));
fd2 = safe_close(fd2);
/* So here's the thing: if we have an O_PATH fd to a symlink, we *cannot* convert it to a regular fd
* with that. i.e. you cannot have the VFS follow a symlink pinned via an O_PATH fd. */
assert_se(fd_reopen(fd1, O_RDONLY|O_CLOEXEC) == -ELOOP);
}
TEST(fd_reopen_condition) {