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Subject[PATCH] dcache: error out on failures to store terminating NUL
Date
A number of routines wasn't checking that the initial call
to prepend "\0" to result buffer doesn't fail.

Coredump code was seeing d_path() with zero-sized buffer
to erroneously return bogus data (non-error pointer
pointing before buffer start).

Users report that this change fixes it.

Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
---
fs/dcache.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 24a01fc..93f651b 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2974,7 +2974,9 @@ char *__d_path(const struct path *path,
char *res = buf + buflen;
int error;

- prepend(&res, &buflen, "\0", 1);
+ error = prepend(&res, &buflen, "\0", 1);
+ if (error)
+ return ERR_PTR(error);
error = prepend_path(path, root, &res, &buflen);

if (error < 0)
@@ -2991,7 +2993,9 @@ char *d_absolute_path(const struct path *path,
char *res = buf + buflen;
int error;

- prepend(&res, &buflen, "\0", 1);
+ error = prepend(&res, &buflen, "\0", 1);
+ if (error)
+ return ERR_PTR(error);
error = prepend_path(path, &root, &res, &buflen);

if (error > 1)
@@ -3008,7 +3012,11 @@ static int path_with_deleted(const struct path *path,
const struct path *root,
char **buf, int *buflen)
{
- prepend(buf, buflen, "\0", 1);
+ int error;
+
+ error = prepend(buf, buflen, "\0", 1);
+ if (error)
+ return error;
if (d_unlinked(path->dentry)) {
int error = prepend(buf, buflen, " (deleted)", 10);
if (error)
@@ -3126,12 +3134,12 @@ static char *__dentry_path(struct dentry *dentry, char *buf, int buflen)
restart:
end = buf + buflen;
len = buflen;
- prepend(&end, &len, "\0", 1);
if (buflen < 1) {
if (!(seq & 1))
rcu_read_unlock();
goto Elong;
}
+ prepend(&end, &len, "\0", 1);
/* Get '/' right */
retval = end-1;
*retval = '/';
@@ -3235,8 +3243,9 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
char *cwd = page + PATH_MAX;
int buflen = PATH_MAX;

- prepend(&cwd, &buflen, "\0", 1);
- error = prepend_path(&pwd, &root, &cwd, &buflen);
+ error = prepend(&cwd, &buflen, "\0", 1);
+ if (!error)
+ error = prepend_path(&pwd, &root, &cwd, &buflen);
rcu_read_unlock();

if (error < 0)
--
1.8.1.4


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