Le 14/04/2020 à 09:01, Christoph Hellwig a écrit :
Currently copy_string_kernel is just a wrapper around copy_strings that
simplifies the calling conventions and uses set_fs to allow passing a
kernel pointer. But due to the fact the we only need to handle a single
kernel argument pointer, the logic can be sigificantly simplified while
getting rid of the set_fs.
Instead of duplicating almost identical code, can you write a function
that takes whether the source is from user or from kernel, then you just
do things like:
if (from_user)
len = strnlen_user(str, MAX_ARG_STRLEN);
else
len = strnlen(str, MAX_ARG_STRLEN);
if (from_user)
copy_from_user(kaddr+offset, str, bytes_to_copy);
else
memcpy(kaddr+offset, str, bytes_to_copy);
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
fs/exec.c | 43 ++++++++++++++++++++++++++++++++++---------
1 file changed, 34 insertions(+), 9 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index b2a77d5acede..ea90af1fb236 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -592,17 +592,42 @@ static int copy_strings(int argc, struct user_arg_ptr argv,
*/
int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
{
- int r;
- mm_segment_t oldfs = get_fs();
- struct user_arg_ptr argv = {
- .ptr.native = (const char __user *const __user *)&arg,
- };
+ int len = strnlen(arg, MAX_ARG_STRLEN) + 1 /* terminating NUL */;
+ unsigned long pos = bprm->p;
+
+ if (len == 0)
+ return -EFAULT;
+ if (!valid_arg_len(bprm, len))
+ return -E2BIG;
+
+ /* We're going to work our way backwards. */
+ arg += len;
+ bprm->p -= len;
+ if (IS_ENABLED(CONFIG_MMU) && bprm->p < bprm->argmin)
+ return -E2BIG;
+
+ while (len > 0) {
+ unsigned int bytes_to_copy = min_t(unsigned int, len,
+ min_not_zero(offset_in_page(pos), PAGE_SIZE));
+ struct page *page;
+ char *kaddr;
- set_fs(KERNEL_DS);
- r = copy_strings(1, argv, bprm);
- set_fs(oldfs);
+ pos -= bytes_to_copy;
+ arg -= bytes_to_copy;
+ len -= bytes_to_copy;
- return r;
+ page = get_arg_page(bprm, pos, 1);
+ if (!page)
+ return -E2BIG;
+ kaddr = kmap_atomic(page);
+ flush_arg_page(bprm, pos & PAGE_MASK, page);
+ memcpy(kaddr + offset_in_page(pos), arg, bytes_to_copy);
+ flush_kernel_dcache_page(page);
+ kunmap_atomic(kaddr);
+ put_arg_page(page);
+ }
+
+ return 0;
}
EXPORT_SYMBOL(copy_string_kernel);
Christophe
