From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 5 Mar 2025 17:08:09 +0000 (-1000)
Subject: fs/pipe: Fix pipe_occupancy() with 16-bit indexes
X-Git-Tag: v6.14-rc6~36
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=c27c66afc449;p=thirdparty%2Flinux.git

fs/pipe: Fix pipe_occupancy() with 16-bit indexes

The pipe_occupancy() logic implicitly relied on the natural unsigned
modulo arithmetic in C, but that doesn't work for the new 'pipe_index_t'
case, since any arithmetic will be done in 'int' (and here we had also
made it 'unsigned int' due to the function call boundary).

So make the modulo arithmetic explicit by casting the result to the
proper type.

Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Swapnil Sapkal <swapnil.sapkal@amd.com>
Cc: Alexey Gladkov <legion@kernel.org>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lore.kernel.org/all/CAHk-=wjyHsGLx=rxg6PKYBNkPYAejgo7=CbyL3=HGLZLsAaJFQ@mail.gmail.com/
Fixes: 3d252160b818 ("fs/pipe: Read pipe->{head,tail} atomically outside pipe->mutex")
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 3cc4f8eab853f..1f013ed7577ef 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -192,7 +192,7 @@ static inline bool pipe_empty(unsigned int head, unsigned int tail)
  */
 static inline unsigned int pipe_occupancy(unsigned int head, unsigned int tail)
 {
-	return head - tail;
+	return (pipe_index_t)(head - tail);
 }
 
 /**