[libc-commits] [libc] [libc] Fix integer overflow for large offsets in lseek. (PR #162394)

[Jackson Stogel via libc-commits]

https://github.com/jtstogel updated https://github.com/llvm/llvm-project/pull/162394

>From b1b84c619a547aea88ec7b41d511c3d973a5c0f0 Mon Sep 17 00:00:00 2001
From: Jackson Stogel <jtstogel at gmail.com>
Date: Tue, 7 Oct 2025 23:06:23 +0000
Subject: [PATCH] [libc] Fix integer overflow for large offsets in lseek.

---
 libc/src/__support/File/linux/lseekImpl.h | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/libc/src/__support/File/linux/lseekImpl.h b/libc/src/__support/File/linux/lseekImpl.h
index c22a6c59b65f1..47df99ae84b90 100644
--- a/libc/src/__support/File/linux/lseekImpl.h
+++ b/libc/src/__support/File/linux/lseekImpl.h
@@ -25,8 +25,9 @@ namespace internal {
 LIBC_INLINE ErrorOr<off_t> lseekimpl(int fd, off_t offset, int whence) {
   off_t result;
 #ifdef SYS_lseek
-  int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_lseek, fd, offset, whence);
-  result = ret;
+  result = LIBC_NAMESPACE::syscall_impl<off_t>(SYS_lseek, fd, offset, whence);
+  if (result < 0)
+    return Error(-static_cast<int>(result));
 #elif defined(SYS_llseek) || defined(SYS__llseek)
   static_assert(sizeof(size_t) == 4, "size_t must be 32 bits.");
 #ifdef SYS_llseek
@@ -37,11 +38,11 @@ LIBC_INLINE ErrorOr<off_t> lseekimpl(int fd, off_t offset, int whence) {
   off_t offset_64 = offset;
   int ret = LIBC_NAMESPACE::syscall_impl<int>(
       LLSEEK_SYSCALL_NO, fd, offset_64 >> 32, offset_64, &result, whence);
+  if (ret < 0)
+    return Error(-ret);
 #else
 #error "lseek, llseek and _llseek syscalls not available."
 #endif
-  if (ret < 0)
-    return Error(-ret);
   return result;
 }