linux-kernel - [PATCH 1/4] elf: don't be afraid of overflow

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Message-ID: <20190204202715.GA27482@avx2>
Date:   Mon, 4 Feb 2019 23:27:15 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] elf: don't be afraid of overflow

Number of ELF program headers is 16-bit by spec, so total size
comfortably fits into "unsigned int".

Space savings: 7 bytes!

	add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-7 (-7)
	Function                                     old     new   delta
	load_elf_phdrs                               137     130      -7

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 fs/binfmt_elf.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -418,8 +418,9 @@ static struct elf_phdr *load_elf_phdrs(struct elfhdr *elf_ex,
 				       struct file *elf_file)
 {
 	struct elf_phdr *elf_phdata = NULL;
-	int retval, size, err = -1;
+	int retval, err = -1;
 	loff_t pos = elf_ex->e_phoff;
+	unsigned int size;
 
 	/*
 	 * If the size of this structure has changed, then punt, since
@@ -429,13 +430,9 @@ static struct elf_phdr *load_elf_phdrs(struct elfhdr *elf_ex,
 		goto out;
 
 	/* Sanity check the number of program headers... */
-	if (elf_ex->e_phnum < 1 ||
-		elf_ex->e_phnum > 65536U / sizeof(struct elf_phdr))
-		goto out;
-
 	/* ...and their total size. */
 	size = sizeof(struct elf_phdr) * elf_ex->e_phnum;
-	if (size > ELF_MIN_ALIGN)
+	if (size == 0 || size > 65536 || size > ELF_MIN_ALIGN)
 		goto out;
 
 	elf_phdata = kmalloc(size, GFP_KERNEL);