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Linux: Rewrite __old_getdents64 [BZ #23497]

Browse Source 
Commit 298d0e3129 ("Consolidate Linux
getdents{64} implementation") broke the implementation because it does
not take into account struct offset differences.

The new implementation is close to the old one, before the
consolidation, but has been cleaned up slightly.
This commit is contained in:
Florian Weimer
2018-08-10 10:20:13 +02:00
parent 8f135efcad
commit 690652882b
4 changed files with 187 additions and 25 deletions
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89
sysdeps/unix/sysv/linux/getdents64.c
View File

@@ -33,41 +33,80 @@ strong_alias (__getdents64, __getdents)
# include <shlib-compat.h>
# if SHLIB_COMPAT(libc, GLIBC_2_1, GLIBC_2_2)
# include <olddirent.h>
# include <olddirent.h>
# include <unistd.h>
/* kernel definition of as of 3.2. */
struct compat_linux_dirent
static ssize_t
handle_overflow (int fd, __off64_t offset, ssize_t count)
{
/* Both d_ino and d_off are compat_ulong_t which are defined in all
architectures as 'u32'. */
uint32_t d_ino;
uint32_t d_off;
unsigned short d_reclen;
char d_name[1];
};
/* If this is the first entry in the buffer, we can report the
error. */
if (count == 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.. */
if (__lseek64 (fd, offset, SEEK_SET) != 0)
return -1;
return count;
}
ssize_t
__old_getdents64 (int fd, char *buf, size_t nbytes)
{
ssize_t retval = INLINE_SYSCALL_CALL (getdents, fd, buf, nbytes);
/* We do not move the individual directory entries. This is only
possible if the target type (struct __old_dirent64) is smaller
than the source type. */
_Static_assert (offsetof (struct __old_dirent64, d_name)
<= offsetof (struct dirent64, d_name),
"__old_dirent64 is larger than dirent64");
_Static_assert (__alignof__ (struct __old_dirent64)
<= __alignof__ (struct dirent64),
"alignment of __old_dirent64 is larger than dirent64");
/* The kernel added the d_type value after the name. Change this now. */
if (retval != -1)
ssize_t retval = INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
if (retval > 0)
{
union
{
struct compat_linux_dirent k;
struct dirent u;
} *kbuf = (void *) buf;
while ((char *) kbuf < buf + retval)
char *p = buf;
char *end = buf + retval;
while (p < end)
{
char d_type = *((char *) kbuf + kbuf->k.d_reclen - 1);
memmove (kbuf->u.d_name, kbuf->k.d_name,
strlen (kbuf->k.d_name) + 1);
kbuf->u.d_type = d_type;
struct dirent64 *source = (struct dirent64 *) p;
kbuf = (void *) ((char *) kbuf + kbuf->k.d_reclen);
/* Copy out the fixed-size data. */
__ino_t ino = source->d_ino;
__off64_t offset = source->d_off;
unsigned int reclen = source->d_reclen;
unsigned char type = source->d_type;
/* Check for ino_t overflow. */
if (__glibc_unlikely (ino != source->d_ino))
return handle_overflow (fd, offset, p - buf);
/* Convert to the target layout. Use a separate struct and
memcpy to side-step aliasing issues. */
struct __old_dirent64 result;
result.d_ino = ino;
result.d_off = offset;
result.d_reclen = reclen;
result.d_type = type;
/* Write the fixed-sized part of the result to the
buffer. */
size_t result_name_offset = offsetof (struct __old_dirent64, d_name);
memcpy (p, &result, result_name_offset);
/* Adjust the position of the name if necessary. Copy
everything until the end of the record, including the
terminating NUL byte. */
if (result_name_offset != offsetof (struct dirent64, d_name))
memmove (p + result_name_offset, source->d_name,
reclen - offsetof (struct dirent64, d_name));
p += reclen;
}
}
return retval;