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mount-util: drop exponential buffer growing in name_to_handle_at_loop()

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So, it appears name_to_handle_at() always returns the right buffer size
on EOVERFLOW, when it's returned due to a too small buffer. Let's rely
on that exclusively for sizing the buffer, and let's drop the
exponential buffer growing.

The new logic is now: if we see EOVERFLOW and the returned size has
increased, resize our buffer and try again. But if it didn't increase,
then propagate the EOVERFLOW as it likely has other causes.
This commit is contained in:
Lennart Poettering 2017-11-23 12:42:24 +01:00
parent 71050acb68
commit fc010b01e7
1 changed files with 11 additions and 10 deletions
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21
src/basic/mount-util.c
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@ -65,7 +65,6 @@ int name_to_handle_at_loop(
for (;;) {
int mnt_id = -1;
size_t m;
if (name_to_handle_at(fd, path, h, &mnt_id, flags) >= 0) {
@ -84,22 +83,24 @@ int name_to_handle_at_loop(
if (!ret_handle && ret_mnt_id && mnt_id >= 0) {
/* As it appears, name_to_handle_at() fills in mnt_id even when it returns EOVERFLOW, but
* that's undocumented. Hence, let's make use of this if it appears to be filled in, and the
* caller was interested in only the mount ID an nothing else. */
/* As it appears, name_to_handle_at() fills in mnt_id even when it returns EOVERFLOW when the
* buffer is too small, but that's undocumented. Hence, let's make use of this if it appears to
* be filled in, and the caller was interested in only the mount ID an nothing else. */
*ret_mnt_id = mnt_id;
return 0;
}
/* The buffer was too small. Size the new buffer by what name_to_handle_at() returned, but make sure it
* is always larger than what we passed in before */
m = h->handle_bytes > n ? h->handle_bytes : n * 2;
if (m < n) /* Check for multiplication overflow */
/* If name_to_handle_at() didn't increase the byte size, then this EOVERFLOW is caused by something
* else (apparently EOVERFLOW is returned for untriggered nfs4 mounts sometimes), not by the too small
* buffer. In that case propagate EOVERFLOW */
if (h->handle_bytes <= n)
return -EOVERFLOW;
if (offsetof(struct file_handle, f_handle) + m < m) /* check for addition overflow */
/* The buffer was too small. Size the new buffer by what name_to_handle_at() returned. */
n = h->handle_bytes;
if (offsetof(struct file_handle, f_handle) + n < n) /* check for addition overflow */
return -EOVERFLOW;
n = m;
free(h);
h = malloc0(offsetof(struct file_handle, f_handle) + n);