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tar: fix race condition

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Problem reported by James Abbatiello in:
https://lists.gnu.org/r/bug-tar/2022-03/msg00000.html
* src/extract.c (make_directories): Do not assume that when
mkdirat fails with errno == EEXIST that there is an existing file
that can be statted.  It could be a dangling symlink.  Instead,
wait until the end and stat it.
This commit is contained in:
Paul Eggert
2022-06-09 22:09:34 -07:00
parent 7a37621e5b
commit 79a442d7b0
2 changed files with 43 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
NEWS
View File

@@ -1,4 +1,4 @@
GNU tar NEWS - User visible changes. 2022-06-09
GNU tar NEWS - User visible changes. 2022-06-10
Please send GNU tar bug reports to <bug-tar@gnu.org>
version 1.34.90 (git)
@@ -28,6 +28,9 @@ version 1.34.90 (git)
** Fix --atime-preserve=replace to not fail if there was no need to replace,
either because we did not read the file, or the atime did not change.
** Fix race when creating a parent directory while another process is
also doing so.
** Fix handling of prefix keywords not followed by "." in pax headers.
** Fix handling of out-of-range sparse entries in pax headers.

61
src/extract.c
View File

@@ -636,8 +636,7 @@ fixup_delayed_set_stat (char const *src, char const *dst)
}
}
/* After a file/link/directory creation has failed, see if
it's because some required directory was not present, and if so,
/* After a file/link/directory creation has failed due to ENOENT,
create all required directories. Return zero if all the required
directories were created, nonzero (issuing a diagnostic) otherwise.
Set *INTERDIR_MADE if at least one directory was created. */
@@ -646,6 +645,8 @@ make_directories (char *file_name, bool *interdir_made)
{
char *cursor0 = file_name + FILE_SYSTEM_PREFIX_LEN (file_name);
char *cursor; /* points into the file name */
char *parent_end = NULL;
int parent_errno;
for (cursor = cursor0; *cursor; cursor++)
{
@@ -685,31 +686,47 @@ make_directories (char *file_name, bool *interdir_made)
print_for_mkdir (file_name, cursor - file_name, desired_mode);
*interdir_made = true;
parent_end = NULL;
}
else if (errno == EEXIST)
status = 0;
else
{
/* Check whether the desired file exists. Even when the
file exists, mkdir can fail with some errno value E other
than EEXIST, so long as E describes an error condition
that also applies. */
int e = errno;
struct stat st;
status = fstatat (chdir_fd, file_name, &st, 0);
if (status)
{
errno = e;
mkdir_error (file_name);
}
}
switch (errno)
{
case ELOOP: case ENAMETOOLONG: case ENOENT: case ENOTDIR:
/* FILE_NAME doesn't exist and couldn't be created; fail now. */
mkdir_error (file_name);
*cursor = '/';
return status;
default:
/* FILE_NAME may be an existing directory so do not fail now.
Instead, arrange to check at loop exit, assuming this is
the last loop iteration. */
parent_end = cursor;
parent_errno = errno;
break;
}
*cursor = '/';
if (status)
return status;
}
return 0;
if (!parent_end)
return 0;
/* Although we did not create the parent directory, some other
process may have created it, so check whether it exists now. */
*parent_end = '\0';
struct stat st;
int stat_status = fstatat (chdir_fd, file_name, &st, 0);
if (!stat_status && !S_ISDIR (st.st_mode))
stat_status = -1;
if (stat_status)
{
errno = parent_errno;
mkdir_error (file_name);
}
*parent_end = '/';
return stat_status;
}
/* Return true if FILE_NAME (with status *STP, if STP) is not a
@@ -824,7 +841,7 @@ maybe_recoverable (char *file_name, bool regular, bool *interdir_made)
case ENOENT:
/* Attempt creating missing intermediate directories. */
if (make_directories (file_name, interdir_made) == 0 && *interdir_made)
if (make_directories (file_name, interdir_made) == 0)
return RECOVER_OK;
break;