Merge pull request #19157 from keszybz/read-medium-sized-virtual-file

basic/fileio: fix reading of not-too-small virtual files

src/basic/fileio.c

@@ -385,20 +385,10 @@ int read_full_virtual_file(const char *filename, char **ret_contents, size_t *re
         if (fd < 0)
                 return -errno;
 
-        /* Start size for files in /proc/ which usually report a file size of 0. (Files in /sys/ report a
-         * file size of 4K, which is probably OK for sizing our initial buffer, and sysfs attributes can't be
-         * larger anyway.)
-         *
-         * It's one less than 4k, so that the malloc() below allocates exactly 4k. */
-        size = 4095;
-
         /* Limit the number of attempts to read the number of bytes returned by fstat(). */
         n_retries = 3;
 
         for (;;) {
-                if (n_retries <= 0)
-                        return -EIO;
-
                 if (fstat(fd, &st) < 0)
                         return -errno;
 
@@ -409,24 +399,20 @@ int read_full_virtual_file(const char *filename, char **ret_contents, size_t *re
                 assert_cc(READ_FULL_BYTES_MAX < SSIZE_MAX);
                 if (st.st_size > 0) {
                         if (st.st_size > READ_FULL_BYTES_MAX)
-                                return -E2BIG;
+                                return -EFBIG;
 
                         size = st.st_size;
                         n_retries--;
                 } else {
-                        /* Double the buffer size */
-                        if (size >= READ_FULL_BYTES_MAX)
-                                return -E2BIG;
-                        if (size > READ_FULL_BYTES_MAX / 2 - 1)
-                                size = READ_FULL_BYTES_MAX; /* clamp to max */
-                        else
-                                size = size * 2 + 1; /* Stay always one less than page size, so we malloc evenly */
+                        size = READ_FULL_BYTES_MAX;
+                        n_retries = 0;
                 }
 
                 buf = malloc(size + 1);
                 if (!buf)
                         return -ENOMEM;
-                size = malloc_usable_size(buf) - 1; /* Use a bigger allocation if we got it anyway */
+                /* Use a bigger allocation if we got it anyway, but not more than the limit. */
+                size = MIN(malloc_usable_size(buf) - 1, READ_FULL_BYTES_MAX);
 
                 for (;;) {
                         ssize_t k;
@@ -453,6 +439,9 @@ int read_full_virtual_file(const char *filename, char **ret_contents, size_t *re
                  * processing, let's try again either with a bigger guessed size or the new
                  * file size. */
 
+                if (n_retries <= 0)
+                        return st.st_size > 0 ? -EIO : -EFBIG;
+
                 if (lseek(fd, 0, SEEK_SET) < 0)
                         return -errno;
 
@@ -466,8 +455,7 @@ int read_full_virtual_file(const char *filename, char **ret_contents, size_t *re
                 p = realloc(buf, n + 1);
                 if (!p)
                         return -ENOMEM;
-
-                buf = TAKE_PTR(p);
+                buf = p;
         }
 
         if (ret_size)

src/test/test-fileio.c

@@ -9,6 +9,7 @@
 #include "ctype.h"
 #include "env-file.h"
 #include "env-util.h"
+#include "errno-util.h"
 #include "fd-util.h"
 #include "fileio.h"
 #include "fs-util.h"
@@ -964,6 +965,24 @@ static void test_read_full_file_offset_size(void) {
         rbuf = mfree(rbuf);
 }
 
+static void test_read_full_virtual_file(void) {
+        const char *filename;
+        int r;
+
+        FOREACH_STRING(filename,
+                       "/proc/1/cmdline",
+                       "/etc/nsswitch.conf",
+                       "/sys/kernel/uevent_seqnum") {
+
+                _cleanup_free_ char *buf = NULL;
+                size_t size = 0;
+
+                r = read_full_virtual_file(filename, &buf, &size);
+                log_info_errno(r, "read_full_virtual_file(\"%s\"): %m (%zu bytes)", filename, size);
+                assert_se(r == 0 || ERRNO_IS_PRIVILEGE(r) || r == -ENOENT);
+        }
+}
+
 int main(int argc, char *argv[]) {
         test_setup_logging(LOG_DEBUG);
 
@@ -991,6 +1010,7 @@ int main(int argc, char *argv[]) {
         test_read_nul_string();
         test_read_full_file_socket();
         test_read_full_file_offset_size();
+        test_read_full_virtual_file();
 
         return 0;
 }