volume_id/fat: careful with sector#, it may not fit in 32 bits. +91 bytes

volume_id/*: a bit of code shrink

1 files changed, 50 insertions, 46 deletions

diff --git a/util-linux/volume_id/util.c b/util-linux/volume_id/util.c
index c4d20ba47..1a1b3f92e 100644
--- a/util-linux/volume_id/util.c
+++ b/util-linux/volume_id/util.c
@@ -195,70 +195,73 @@ set:
  * It's better to ignore such fs and continue.  */
 void *volume_id_get_buffer(struct volume_id *id, uint64_t off, size_t len)
 {
-        ssize_t buf_len;
+        uint8_t *dst;
+        unsigned small_off;
+        ssize_t read_len;
+
+        dbg("get buffer off 0x%llx(%llu), len 0x%zx",
+                (unsigned long long) off, (unsigned long long) off, len);
 
-        dbg("get buffer off 0x%llx(%llu), len 0x%zx", (unsigned long long) off, (unsigned long long) off, len);
         /* check if requested area fits in superblock buffer */
-        if (off + len <= SB_BUFFER_SIZE) {
+        if (off + len <= SB_BUFFER_SIZE
+         /* && off <= SB_BUFFER_SIZE - want this paranoid overflow check? */
+        ) {
                 if (id->sbbuf == NULL) {
                         id->sbbuf = xmalloc(SB_BUFFER_SIZE);
                 }
+                small_off = off;
+                dst = id->sbbuf;
 
                 /* check if we need to read */
-                if ((off + len) > id->sbbuf_len) {
-                        dbg("read sbbuf len:0x%llx", (unsigned long long) (off + len));
-                        if (lseek(id->fd, 0, SEEK_SET) != 0) {
-                                dbg("seek(0) failed");
-                                return NULL;
-                        }
-                        buf_len = full_read(id->fd, id->sbbuf, off + len);
-                        if (buf_len < 0) {
-                                dbg("read failed (%s)", strerror(errno));
-                                return NULL;
-                        }
-                        dbg("got 0x%zx (%zi) bytes", buf_len, buf_len);
-                        id->sbbuf_len = buf_len;
-                        if ((uint64_t)buf_len < off + len) {
-                                dbg("requested 0x%zx bytes, got only 0x%zx bytes", len, buf_len);
-                                return NULL;
-                        }
-                }
+                len += off;
+                if (len <= id->sbbuf_len)
+                        goto ret; /* we already have it */
 
-                return &(id->sbbuf[off]);
+                dbg("read sbbuf len:0x%x", (unsigned) len);
+                id->sbbuf_len = len;
+                off = 0;
+                goto do_read;
         }
 
         if (len > SEEK_BUFFER_SIZE) {
                 dbg("seek buffer too small %d", SEEK_BUFFER_SIZE);
                 return NULL;
         }
-
-        /* get seek buffer */
-        if (id->seekbuf == NULL) {
-                id->seekbuf = xmalloc(SEEK_BUFFER_SIZE);
-        }
+        dst = id->seekbuf;
 
         /* check if we need to read */
-        if ((off < id->seekbuf_off) || ((off + len) > (id->seekbuf_off + id->seekbuf_len))) {
-                dbg("read seekbuf off:0x%llx len:0x%zx", (unsigned long long) off, len);
-                if (lseek(id->fd, off, SEEK_SET) != off) {
-                        dbg("seek(0x%llx) failed", (unsigned long long) off);
-                        return NULL;
-                }
-                buf_len = full_read(id->fd, id->seekbuf, len);
-                if (buf_len < 0) {
-                        dbg("read failed (%s)", strerror(errno));
-                        return NULL;
-                }
-                dbg("got 0x%zx (%zi) bytes", buf_len, buf_len);
-                id->seekbuf_off = off;
-                id->seekbuf_len = buf_len;
-                if ((size_t)buf_len < len) {
-                        dbg("requested 0x%zx bytes, got only 0x%zx bytes", len, buf_len);
-                        return NULL;
-                }
+        if ((off >= id->seekbuf_off)
+         && ((off + len) <= (id->seekbuf_off + id->seekbuf_len))
+        ) {
+                small_off = off - id->seekbuf_off; /* can't overflow */
+                goto ret; /* we already have it */
         }
 
-        return &(id->seekbuf[off - id->seekbuf_off]);
+        id->seekbuf_off = off;
+        id->seekbuf_len = len;
+        id->seekbuf = xrealloc(id->seekbuf, len);
+        small_off = 0;
+        dst = id->seekbuf;
+        dbg("read seekbuf off:0x%llx len:0x%zx",
+                                (unsigned long long) off, len);
+ do_read:
+        if (lseek(id->fd, off, SEEK_SET) != off) {
+                dbg("seek(0x%llx) failed", (unsigned long long) off);
+                goto err;
+        }
+        read_len = full_read(id->fd, dst, len);
+        if (read_len != len) {
+                dbg("requested 0x%x bytes, got 0x%x bytes",
+                                (unsigned) len, (unsigned) read_len);
+ err:
+                /* id->seekbuf_len or id->sbbuf_len is wrong now! Fixing.
+                 * Most likely user will not do any additional
+                 * calls anyway, it's a corrupted fs or something. */
+                volume_id_free_buffer(id);
+                return NULL;
+        }
+ ret:
+        return dst + small_off;
 }
 
 void volume_id_free_buffer(struct volume_id *id)
@@ -269,4 +272,5 @@ void volume_id_free_buffer(struct volume_id *id)
         free(id->seekbuf);
         id->seekbuf = NULL;
         id->seekbuf_len = 0;
+        id->seekbuf_off = 0; /* paranoia */
 }