Merge pull request #31419 from AdrianVovk/fixup-largefile-define

Fixup largefile define

src/basic/fd-util.h

@@ -8,6 +8,7 @@
 #include <sys/socket.h>
 
 #include "macro.h"
+#include "missing_fcntl.h"
 #include "stdio-util.h"
 
 /* maximum length of fdname */
@@ -21,6 +22,20 @@
 #define EBADF_PAIR { -EBADF, -EBADF }
 #define EBADF_TRIPLET { -EBADF, -EBADF, -EBADF }
 
+/* Flags that are safe to have set on an FD given to a privileged service to operate on.
+ * This ensures that clients can't trick a privileged service into giving access to a file the client
+ * doesn't already have access to (especially via something like O_PATH).
+ *
+ * O_NOFOLLOW: For some reason the kernel will return this flag from fcntl; it doesn't go away immediately
+ *             after open(). It should have no effect whatsoever to an already-opened FD, but if it does
+ *             it's decreasing the risk to a privileged service since it disables symlink following.
+ *
+ * RAW_O_LARGEFILE: glibc secretly sets this and neglects to hide it from us if we call fcntl. See comment
+ *                  in missing_fcntl.h for more details about this.
+ */
+#define SAFE_FD_FLAGS (O_ACCMODE|O_NOFOLLOW|RAW_O_LARGEFILE)
+#define UNSAFE_FD_FLAGS(flags) ((unsigned)(flags) & ~SAFE_FD_FLAGS)
+
 int close_nointr(int fd);
 int safe_close(int fd);
 void safe_close_pair(int p[static 2]);

src/basic/missing_fcntl.h

@@ -69,9 +69,26 @@
 
 /* So O_LARGEFILE is generally implied by glibc, and defined to zero hence, because we only build in LFS
  * mode. However, when invoking fcntl(F_GETFL) the flag is ORed into the result anyway — glibc does not mask
- * it away. Which sucks. Let's define the actual value here, so that we can mask it ourselves. */
+ * it away. Which sucks. Let's define the actual value here, so that we can mask it ourselves.
+ *
+ * The precise definition is arch specific, so we use the values defined in the kernel (note that some
+ * are hexa and others are octal; duplicated as-is from the kernel definitions):
+ * - alpha, arm, arm64, m68k, mips, parisc, powerpc, sparc: each has a specific value;
+ * - others: they use the "generic" value (defined in include/uapi/asm-generic/fcntl.h) */
 #if O_LARGEFILE != 0
 #define RAW_O_LARGEFILE O_LARGEFILE
 #else
-#define RAW_O_LARGEFILE 0100000
+#if defined(__alpha__) || defined(__arm__) || defined(__aarch64__) || defined(__m68k__)
+#define RAW_O_LARGEFILE 0400000
+#elif defined(__mips__)
+#define RAW_O_LARGEFILE 0x2000
+#elif defined(__parisc__) || defined(__hppa__)
+#define RAW_O_LARGEFILE 000004000
+#elif defined(__powerpc__)
+#define RAW_O_LARGEFILE 0200000
+#elif defined(__sparc__)
+#define RAW_O_LARGEFILE 0x40000
+#else
+#define RAW_O_LARGEFILE 00100000
+#endif
 #endif

src/home/homed-bus.c

@@ -3,7 +3,6 @@
 #include "fd-util.h"
 #include "home-util.h"
 #include "homed-bus.h"
-#include "missing_fcntl.h"
 #include "stat-util.h"
 #include "strv.h"
 
@@ -120,8 +119,10 @@ int bus_message_read_blobs(sd_bus_message *m, Hashmap **ret, sd_bus_error *error
 
                 /* Refuse fds w/ unexpected flags set. In particular, we don't want to permit O_PATH FDs, since
                  * those don't actually guarantee that the client has access to the file. */
-                if ((flags & ~(O_ACCMODE|RAW_O_LARGEFILE)) != 0)
-                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "FD for %s has unexpected flags set", filename);
+                if (UNSAFE_FD_FLAGS(flags) != 0)
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
+                                                 "FD for %s has unexpected flags set: 0%o",
+                                                 filename, UNSAFE_FD_FLAGS(flags));
 
                 r = hashmap_put(blobs, filename, FD_TO_PTR(fd));
                 if (r < 0)

src/journal/journald-native.c

@@ -22,7 +22,6 @@
 #include "journald-wall.h"
 #include "memfd-util.h"
 #include "memory-util.h"
-#include "missing_fcntl.h"
 #include "parse-util.h"
 #include "path-util.h"
 #include "process-util.h"
@@ -363,8 +362,10 @@ void server_process_native_file(
                 return;
         }
 
-        if ((flags & ~(O_ACCMODE|RAW_O_LARGEFILE)) != 0) {
-                log_ratelimit_error(JOURNAL_LOG_RATELIMIT, "Unexpected flags of passed memory fd, ignoring message: %m");
+        if (UNSAFE_FD_FLAGS(flags) != 0) {
+                log_ratelimit_error(JOURNAL_LOG_RATELIMIT,
+                                    "Unexpected flags of passed memory fd (0%o), ignoring message: %m",
+                                    UNSAFE_FD_FLAGS(flags));
                 return;
         }