Patchwork [v11,06/14] fs, arm64: untag user pointers in copy_mount_options

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Submitter Andrey Konovalov
Date March 15, 2019, 7:51 p.m.
Message ID <e12d6b5008f63b530d25ad73b2e3491939005c22.1552679409.git.andreyknvl@google.com>
Download mbox | patch
Permalink /patch/749953/
State New
Headers show

Comments

Andrey Konovalov - March 15, 2019, 7:51 p.m.
This patch is a part of a series that extends arm64 kernel ABI to allow to
pass tagged user pointers (with the top byte set to something else other
than 0x00) as syscall arguments.

In copy_mount_options a user address is being subtracted from TASK_SIZE.
If the address is lower than TASK_SIZE, the size is calculated to not
allow the exact_copy_from_user() call to cross TASK_SIZE boundary.
However if the address is tagged, then the size will be calculated
incorrectly.

Untag the address before subtracting.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 fs/namespace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

diff --git a/fs/namespace.c b/fs/namespace.c
index c9cab307fa77..c27e5713bf04 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2825,7 +2825,7 @@  void *copy_mount_options(const void __user * data)
 	 * the remainder of the page.
 	 */
 	/* copy_from_user cannot cross TASK_SIZE ! */
-	size = TASK_SIZE - (unsigned long)data;
+	size = TASK_SIZE - (unsigned long)untagged_addr(data);
 	if (size > PAGE_SIZE)
 		size = PAGE_SIZE;