From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Jackson Subject: [PATCH 12/22] libelf: Check pointer references in elf_is_elfbinary Date: Tue, 11 Jun 2013 19:20:55 +0100 Message-ID: <1370974865-19554-13-git-send-email-ian.jackson@eu.citrix.com> References: <1370974865-19554-1-git-send-email-ian.jackson@eu.citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1370974865-19554-1-git-send-email-ian.jackson@eu.citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: xen-devel@lists.xensource.com Cc: andrew.cooper3@citrix.com, mattjd@gmail.com, Ian Jackson , security@xen.org List-Id: xen-devel@lists.xenproject.org elf_is_elfbinary didn't take a length parameter and could potentially access out of range when provided with a very short image. We only need to check the size is enough for the actual dereference in elf_is_elfbinary; callers are just using it to check the magic number and do their own checks (usually via the new elf_ptrval system) before dereferencing other parts of the header. This is part of the fix to a security issue, XSA-55. Signed-off-by: Ian Jackson Acked-by: Ian Campbell Reviewed-by: Konrad Rzeszutek Wilk v7: Add a comment about the limited function of elf_is_elfbinary. v2: Style fix. Fix commit message subject. --- tools/libxc/xc_dom_elfloader.c | 2 +- xen/arch/x86/bzimage.c | 4 ++-- xen/common/libelf/libelf-loader.c | 2 +- xen/common/libelf/libelf-tools.c | 9 ++++++--- xen/include/xen/libelf.h | 4 +++- 5 files changed, 13 insertions(+), 8 deletions(-) diff --git a/tools/libxc/xc_dom_elfloader.c b/tools/libxc/xc_dom_elfloader.c index c038d1c..f14b053 100644 --- a/tools/libxc/xc_dom_elfloader.c +++ b/tools/libxc/xc_dom_elfloader.c @@ -93,7 +93,7 @@ static int check_elf_kernel(struct xc_dom_image *dom, int verbose) return -EINVAL; } - if ( !elf_is_elfbinary(dom->kernel_blob) ) + if ( !elf_is_elfbinary(dom->kernel_blob, dom->kernel_size) ) { if ( verbose ) xc_dom_panic(dom->xch, diff --git a/xen/arch/x86/bzimage.c b/xen/arch/x86/bzimage.c index c5519d8..58fda16 100644 --- a/xen/arch/x86/bzimage.c +++ b/xen/arch/x86/bzimage.c @@ -220,7 +220,7 @@ unsigned long __init bzimage_headroom(char *image_start, image_length = hdr->payload_length; } - if ( elf_is_elfbinary(image_start) ) + if ( elf_is_elfbinary(image_start, image_length) ) return 0; orig_image_len = image_length; @@ -251,7 +251,7 @@ int __init bzimage_parse(char *image_base, char **image_start, unsigned long *im *image_len = hdr->payload_length; } - if ( elf_is_elfbinary(*image_start) ) + if ( elf_is_elfbinary(*image_start, *image_len) ) return 0; BUG_ON(!(image_base < *image_start)); diff --git a/xen/common/libelf/libelf-loader.c b/xen/common/libelf/libelf-loader.c index 878552e..6c43c34 100644 --- a/xen/common/libelf/libelf-loader.c +++ b/xen/common/libelf/libelf-loader.c @@ -29,7 +29,7 @@ int elf_init(struct elf_binary *elf, const char *image_input, size_t size) ELF_HANDLE_DECL(elf_shdr) shdr; uint64_t i, count, section, offset; - if ( !elf_is_elfbinary(image_input) ) + if ( !elf_is_elfbinary(image_input, size) ) { elf_err(elf, "%s: not an ELF binary\n", __FUNCTION__); return -1; diff --git a/xen/common/libelf/libelf-tools.c b/xen/common/libelf/libelf-tools.c index 08ab027..b613593 100644 --- a/xen/common/libelf/libelf-tools.c +++ b/xen/common/libelf/libelf-tools.c @@ -332,11 +332,14 @@ ELF_HANDLE_DECL(elf_note) elf_note_next(struct elf_binary *elf, ELF_HANDLE_DECL( /* ------------------------------------------------------------------------ */ -int elf_is_elfbinary(const void *image) +int elf_is_elfbinary(const void *image_start, size_t image_size) { - const Elf32_Ehdr *ehdr = image; + const Elf32_Ehdr *ehdr = image_start; - return IS_ELF(*ehdr); /* fixme unchecked */ + if ( image_size < sizeof(*ehdr) ) + return 0; + + return IS_ELF(*ehdr); } int elf_phdr_is_loadable(struct elf_binary *elf, ELF_HANDLE_DECL(elf_phdr) phdr) diff --git a/xen/include/xen/libelf.h b/xen/include/xen/libelf.h index f3f18da..df93f2c 100644 --- a/xen/include/xen/libelf.h +++ b/xen/include/xen/libelf.h @@ -350,7 +350,9 @@ uint64_t elf_note_numeric_array(struct elf_binary *, ELF_HANDLE_DECL(elf_note), unsigned int unitsz, unsigned int idx); ELF_HANDLE_DECL(elf_note) elf_note_next(struct elf_binary *elf, ELF_HANDLE_DECL(elf_note) note); -int elf_is_elfbinary(const void *image); +/* (Only) checks that the image has the right magic number. */ +int elf_is_elfbinary(const void *image_start, size_t image_size); + int elf_phdr_is_loadable(struct elf_binary *elf, ELF_HANDLE_DECL(elf_phdr) phdr); /* ------------------------------------------------------------------------ */ -- 1.7.2.5