Discussion:
[PATCH] compat getdents64: Use correct offset for retry [BZ #23972]
(too old to reply)
Florian Weimer
2018-12-10 13:28:04 UTC
Permalink
d_off is the offset of the *next* entry, not the offset of the current
entry.

2018-12-10 Florian Weimer <***@redhat.com>

[BZ #23972]
* sysdeps/unix/sysv/linux/getdents64.c (handle_overflow): Check
offset instead of count for clarity. Fix typo in comment.
(__old_getdents64): Keep track of previous offset. Use it to call
handle_overflow.
* sysdeps/unix/sysv/linux/tst-readdir64-compat.c (do_test): Check
that d_off is never zero.

diff --git a/sysdeps/unix/sysv/linux/getdents64.c b/sysdeps/unix/sysv/linux/getdents64.c
index bc140b5a7f..46eb5f4419 100644
--- a/sysdeps/unix/sysv/linux/getdents64.c
+++ b/sysdeps/unix/sysv/linux/getdents64.c
@@ -41,14 +41,14 @@ handle_overflow (int fd, __off64_t offset, ssize_t count)
{
/* If this is the first entry in the buffer, we can report the
error. */
- if (count == 0)
+ if (offset == 0)
{
__set_errno (EOVERFLOW);
return -1;
}

/* Otherwise, seek to the overflowing entry, so that the next call
- will report the error, and return the data read so far.. */
+ will report the error, and return the data read so far. */
if (__lseek64 (fd, offset, SEEK_SET) != 0)
return -1;
return count;
@@ -70,6 +70,15 @@ __old_getdents64 (int fd, char *buf, size_t nbytes)
ssize_t retval = INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
if (retval > 0)
{
+ /* This is the marker for the first entry. Offset 0 is reserved
+ for the first entry (see rewinddir). Here, we use it as a
+ marker for the first entry in the buffer. We never actually
+ seek to offset 0 because handle_overflow reports the error
+ directly, so it does not matter that the offset is incorrect
+ if entries have been read from the descriptor before (so that
+ the descriptor is not actually at offset 0). */
+ __off64_t previous_offset = 0;
+
char *p = buf;
char *end = buf + retval;
while (p < end)
@@ -84,7 +93,7 @@ __old_getdents64 (int fd, char *buf, size_t nbytes)

/* Check for ino_t overflow. */
if (__glibc_unlikely (ino != source->d_ino))
- return handle_overflow (fd, offset, p - buf);
+ return handle_overflow (fd, previous_offset, p - buf);

/* Convert to the target layout. Use a separate struct and
memcpy to side-step aliasing issues. */
@@ -107,6 +116,7 @@ __old_getdents64 (int fd, char *buf, size_t nbytes)
reclen - offsetof (struct dirent64, d_name));

p += reclen;
+ previous_offset = offset;
}
}
return retval;
diff --git a/sysdeps/unix/sysv/linux/tst-readdir64-compat.c b/sysdeps/unix/sysv/linux/tst-readdir64-compat.c
index 43c4a8477c..cb78bc9be4 100644
--- a/sysdeps/unix/sysv/linux/tst-readdir64-compat.c
+++ b/sysdeps/unix/sysv/linux/tst-readdir64-compat.c
@@ -88,6 +88,10 @@ do_test (void)
else
TEST_VERIFY_EXIT (entry_test != NULL);

+ /* d_off is never zero because it is the offset of the next
+ entry (not the current entry). */
+ TEST_VERIFY (entry_reference->d_off > 0);
+
/* Check that the entries are the same. */
TEST_COMPARE_BLOB (entry_reference->d_name,
strlen (entry_reference->d_name),
Andreas Schwab
2018-12-10 15:11:50 UTC
Permalink
Post by Florian Weimer
[BZ #23972]
* sysdeps/unix/sysv/linux/getdents64.c (handle_overflow): Check
offset instead of count for clarity. Fix typo in comment.
(__old_getdents64): Keep track of previous offset. Use it to call
handle_overflow.
* sysdeps/unix/sysv/linux/tst-readdir64-compat.c (do_test): Check
that d_off is never zero.
Ok.

Andreas.
--
Andreas Schwab, SUSE Labs, ***@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."
Loading...