linux-kernel - [PATCH 5/7] binfmt_elf: remove the set_fs in fill_siginfo

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Date:   Tue,  5 May 2020 12:12:54 +0200
From:   Christoph Hellwig <hch@....de>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Jeremy Kerr <jk@...abs.org>, Arnd Bergmann <arnd@...db.de>,
        Oleg Nesterov <oleg@...hat.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>, x86@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 5/7] binfmt_elf: remove the set_fs in fill_siginfo_note

From: "Eric W. Biederman" <ebiederm@...ssion.com>

The code in binfmt_elf.c is differnt from the rest of the code that
processes siginfo, as it sends siginfo from a kernel buffer to a file
rather than from kernel memory to userspace buffers.  To remove it's
use of set_fs the code needs some different siginfo helpers.

Add the helper copy_siginfo_to_external to copy from the kernel's
internal siginfo layout to a buffer in the siginfo layout that
userspace expects.

Modify fill_siginfo_note to use copy_siginfo_to_external instead of
set_fs and copy_siginfo_to_user.

Update compat_binfmt_elf.c to use the previously added
copy_siginfo_to_external32 to handle the compat case.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Christoph Hellwig <hch@....de>
---
 fs/binfmt_elf.c        | 5 +----
 fs/compat_binfmt_elf.c | 2 +-
 include/linux/signal.h | 8 ++++++++
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 13f25e241ac46..a1f57e20c3cf2 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1556,10 +1556,7 @@ static void fill_auxv_note(struct memelfnote *note, struct mm_struct *mm)
 static void fill_siginfo_note(struct memelfnote *note, user_siginfo_t *csigdata,
 		const kernel_siginfo_t *siginfo)
 {
-	mm_segment_t old_fs = get_fs();
-	set_fs(KERNEL_DS);
-	copy_siginfo_to_user((user_siginfo_t __user *) csigdata, siginfo);
-	set_fs(old_fs);
+	copy_siginfo_to_external(csigdata, siginfo);
 	fill_note(note, "CORE", NT_SIGINFO, sizeof(*csigdata), csigdata);
 }
 
diff --git a/fs/compat_binfmt_elf.c b/fs/compat_binfmt_elf.c
index aaad4ca1217ef..fa0e24e1b7267 100644
--- a/fs/compat_binfmt_elf.c
+++ b/fs/compat_binfmt_elf.c
@@ -39,7 +39,7 @@
  */
 #define user_long_t		compat_long_t
 #define user_siginfo_t		compat_siginfo_t
-#define copy_siginfo_to_user	copy_siginfo_to_user32
+#define copy_siginfo_to_external	copy_siginfo_to_external32
 
 /*
  * The machine-dependent core note format types are defined in elfcore-compat.h,
diff --git a/include/linux/signal.h b/include/linux/signal.h
index 05bacd2ab1350..6bb1a3f0258c2 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -24,6 +24,14 @@ static inline void clear_siginfo(kernel_siginfo_t *info)
 
 #define SI_EXPANSION_SIZE (sizeof(struct siginfo) - sizeof(struct kernel_siginfo))
 
+static inline void copy_siginfo_to_external(siginfo_t *to,
+					    const kernel_siginfo_t *from)
+{
+	memcpy(to, from, sizeof(*from));
+	memset(((char *)to) + sizeof(struct kernel_siginfo), 0,
+		SI_EXPANSION_SIZE);
+}
+
 int copy_siginfo_to_user(siginfo_t __user *to, const kernel_siginfo_t *from);
 int copy_siginfo_from_user(kernel_siginfo_t *to, const siginfo_t __user *from);
 
-- 
2.26.2