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authorNick Piggin <npiggin@suse.de>2007-05-08 00:25:16 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-05-08 11:15:00 -0700
commit4fc75ff4816c3483b4b772b2f6cb3d8fd88ca547 (patch)
treef2169f152113af815e69d74ca40c282439e7c3f6
parentaf7c693f146069a1f44739acef9abf1bc27f7247 (diff)
exec: fix remove_arg_zero
Petr Tesarik discovered a problem in remove_arg_zero(). He writes: When a script is loaded, load_script() replaces argv[0] with the name of the interpreter and the filename passed to the exec syscall. However, there is no guarantee that the length of the interpreter name plus the length of the filename is greater than the length of the original argv[0]. If the difference happens to cross a page boundary, setup_arg_pages() will call put_dirty_page() [aka install_arg_page()] with an address outside the VMA. Therefore, remove_arg_zero() must free all pages which would be unused after the argument is removed. So, rewrite the remove_arg_zero function without gotos, with a few comments, and with the commonly used explicit index/offset. This fixes the problem and makes it easier to understand as well. [a.p.zijlstra@chello.nl: add comment] Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Petr Tesarik <ptesarik@suse.cz> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/exec.c50
1 files changed, 34 insertions, 16 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 3155e915307a..f1691cd0c9d2 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -982,33 +982,51 @@ void compute_creds(struct linux_binprm *bprm)
task_unlock(current);
security_bprm_post_apply_creds(bprm);
}
-
EXPORT_SYMBOL(compute_creds);
+/*
+ * Arguments are '\0' separated strings found at the location bprm->p
+ * points to; chop off the first by relocating brpm->p to right after
+ * the first '\0' encountered.
+ */
void remove_arg_zero(struct linux_binprm *bprm)
{
if (bprm->argc) {
- unsigned long offset;
- char * kaddr;
- struct page *page;
+ char ch;
- offset = bprm->p % PAGE_SIZE;
- goto inside;
+ do {
+ unsigned long offset;
+ unsigned long index;
+ char *kaddr;
+ struct page *page;
- while (bprm->p++, *(kaddr+offset++)) {
- if (offset != PAGE_SIZE)
- continue;
- offset = 0;
- kunmap_atomic(kaddr, KM_USER0);
-inside:
- page = bprm->page[bprm->p/PAGE_SIZE];
+ offset = bprm->p & ~PAGE_MASK;
+ index = bprm->p >> PAGE_SHIFT;
+
+ page = bprm->page[index];
kaddr = kmap_atomic(page, KM_USER0);
- }
- kunmap_atomic(kaddr, KM_USER0);
+
+ /* run through page until we reach end or find NUL */
+ do {
+ ch = *(kaddr + offset);
+
+ /* discard that character... */
+ bprm->p++;
+ offset++;
+ } while (offset < PAGE_SIZE && ch != '\0');
+
+ kunmap_atomic(kaddr, KM_USER0);
+
+ /* free the old page */
+ if (offset == PAGE_SIZE) {
+ __free_page(page);
+ bprm->page[index] = NULL;
+ }
+ } while (ch != '\0');
+
bprm->argc--;
}
}
-
EXPORT_SYMBOL(remove_arg_zero);
/*