From: Nick Piggin 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. Signed-off-by: Nick Piggin Cc: Petr Tesarik Signed-off-by: Andrew Morton --- fs/exec.c | 43 +++++++++++++++++++++++++++++-------------- 1 file changed, 29 insertions(+), 14 deletions(-) diff -puN fs/exec.c~exec-fix-remove_arg_zero fs/exec.c --- a/fs/exec.c~exec-fix-remove_arg_zero +++ a/fs/exec.c @@ -988,23 +988,38 @@ EXPORT_SYMBOL(compute_creds); 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--; } } _