Re: [PATCH] strings: Produce error when section data falls outside file.

Re: [PATCH] strings: Produce error when section data falls outside file.

[Alexander Cherepanov]

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On 2014-12-27 01:00, Mark Wielaard wrote:
> diff --git a/src/strings.c b/src/strings.c
> index f60e4b4..d1eb7b2 100644
> --- a/src/strings.c
> +++ b/src/strings.c
> @@ -725,8 +725,21 @@ read_elf (Elf *elf, int fd, const char *fname, off64_t fdlen)
>   	 actually have content.  */
>         if (shdr != NULL && shdr->sh_type != SHT_NOBITS
>   	  && (shdr->sh_flags & SHF_ALLOC) != 0)
> -	result |= read_block (fd, fname, fdlen, shdr->sh_offset,
> -			      shdr->sh_offset + shdr->sh_size);
> +	{
> +	  if (shdr->sh_offset > fdlen
> +	      || fdlen - shdr->sh_offset < shdr->sh_size)
> +	    {

It fails to build for me:

strings.c: In function 'read_elf':
strings.c:729:24: error: comparison between signed and unsigned integer 
expressions [-Werror=sign-compare]
     if (shdr->sh_offset > fdlen
                         ^
cc1: all warnings being treated as errors

-- 
Alexander Cherepanov

Re: [PATCH] strings: Produce error when section data falls outside file.

[Mark Wielaard]

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On Mon, 2014-12-29 at 01:15 +0300, Alexander Cherepanov wrote:
> On 2014-12-27 14:42, Mark Wielaard wrote:
> > On Sat, Dec 27, 2014 at 04:31:14AM +0300, Alexander Cherepanov wrote:
> >> strings.c: In function 'read_elf':
> >> strings.c:729:24: error: comparison between signed and unsigned integer
> >> expressions [-Werror=sign-compare]
> >>      if (shdr->sh_offset > fdlen
> >
> > The compiler is correct. sh_offset is an unsigned Elf64_Off and fdlen is
> > a signed off64_t. But just before we already checked fdlen >= 0, so we
> 
> I see.
> 
> > can just cast it to Elf64_Off safely for this comparison. As attached.
> 
> Thanks, mjw/pending is compiling fine now.

Thanks for double checking. I pushed that patch to master now.

Re: [PATCH] strings: Produce error when section data falls outside file.

[Alexander Cherepanov]

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On 2014-12-27 14:42, Mark Wielaard wrote:
> On Sat, Dec 27, 2014 at 04:31:14AM +0300, Alexander Cherepanov wrote:
>> On 2014-12-27 01:00, Mark Wielaard wrote:
>>> diff --git a/src/strings.c b/src/strings.c
>>> index f60e4b4..d1eb7b2 100644
>>> --- a/src/strings.c
>>> +++ b/src/strings.c
>>> @@ -725,8 +725,21 @@ read_elf (Elf *elf, int fd, const char *fname, off64_t fdlen)
>>>   	 actually have content.  */
>>>         if (shdr != NULL && shdr->sh_type != SHT_NOBITS
>>>   	  && (shdr->sh_flags & SHF_ALLOC) != 0)
>>> -	result |= read_block (fd, fname, fdlen, shdr->sh_offset,
>>> -			      shdr->sh_offset + shdr->sh_size);
>>> +	{
>>> +	  if (shdr->sh_offset > fdlen
>>> +	      || fdlen - shdr->sh_offset < shdr->sh_size)
>>> +	    {
>>
>> It fails to build for me:
>>
>> strings.c: In function 'read_elf':
>> strings.c:729:24: error: comparison between signed and unsigned integer
>> expressions [-Werror=sign-compare]
>>      if (shdr->sh_offset > fdlen
>
> The compiler is correct. sh_offset is an unsigned Elf64_Off and fdlen is
> a signed off64_t. But just before we already checked fdlen >= 0, so we

I see.

> can just cast it to Elf64_Off safely for this comparison. As attached.

Thanks, mjw/pending is compiling fine now.

-- 
Alexander Cherepanov

Re: [PATCH] strings: Produce error when section data falls outside file.

[Mark Wielaard]

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On Sat, Dec 27, 2014 at 04:31:14AM +0300, Alexander Cherepanov wrote:
> On 2014-12-27 01:00, Mark Wielaard wrote:
> >diff --git a/src/strings.c b/src/strings.c
> >index f60e4b4..d1eb7b2 100644
> >--- a/src/strings.c
> >+++ b/src/strings.c
> >@@ -725,8 +725,21 @@ read_elf (Elf *elf, int fd, const char *fname, off64_t fdlen)
> >  	 actually have content.  */
> >        if (shdr != NULL && shdr->sh_type != SHT_NOBITS
> >  	  && (shdr->sh_flags & SHF_ALLOC) != 0)
> >-	result |= read_block (fd, fname, fdlen, shdr->sh_offset,
> >-			      shdr->sh_offset + shdr->sh_size);
> >+	{
> >+	  if (shdr->sh_offset > fdlen
> >+	      || fdlen - shdr->sh_offset < shdr->sh_size)
> >+	    {
> 
> It fails to build for me:
> 
> strings.c: In function 'read_elf':
> strings.c:729:24: error: comparison between signed and unsigned integer
> expressions [-Werror=sign-compare]
>     if (shdr->sh_offset > fdlen

The compiler is correct. sh_offset is an unsigned Elf64_Off and fdlen is
a signed off64_t. But just before we already checked fdlen >= 0, so we
can just cast it to Elf64_Off safely for this comparison. As attached.

Thanks,

Mark

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>From 37497cb28139057a5413f9592b6ceb3a06c41482 Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mjw@redhat.com>
Date: Fri, 26 Dec 2014 22:57:00 +0100
Subject: [PATCH] strings: Produce error when section data falls outside file.

https://bugzilla.redhat.com/show_bug.cgi?id=1170810

Reported-by: Alexander Cherepanov <cherepan@mccme.ru>
Signed-off-by: Mark Wielaard <mjw@redhat.com>
---
 src/ChangeLog |  5 +++++
 src/strings.c | 17 +++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/ChangeLog b/src/ChangeLog
index 904b3c9..66d6270 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,10 @@
 2014-12-26  Mark Wielaard  <mjw@redhat.com>
 
+	* strings.c (read_elf): Produce error when section data falls outside
+	file.
+
+2014-12-26  Mark Wielaard  <mjw@redhat.com>
+
 	* nm.c (show_symbols): Guard against divide by zero in error check.
 	Add section index number in error message.
 
diff --git a/src/strings.c b/src/strings.c
index f60e4b4..b2bce7b 100644
--- a/src/strings.c
+++ b/src/strings.c
@@ -725,8 +725,21 @@ read_elf (Elf *elf, int fd, const char *fname, off64_t fdlen)
 	 actually have content.  */
       if (shdr != NULL && shdr->sh_type != SHT_NOBITS
 	  && (shdr->sh_flags & SHF_ALLOC) != 0)
-	result |= read_block (fd, fname, fdlen, shdr->sh_offset,
-			      shdr->sh_offset + shdr->sh_size);
+	{
+	  if (shdr->sh_offset > (Elf64_Off) fdlen
+	      || fdlen - shdr->sh_offset < shdr->sh_size)
+	    {
+	      size_t strndx = 0;
+	      elf_getshdrstrndx (elf, &strndx);
+	      error (0, 0,
+		     gettext ("Skipping section %zd '%s' data outside file"),
+		     elf_ndxscn (scn), elf_strptr (elf, strndx, shdr->sh_name));
+	      result = 1;
+	    }
+	  else
+	    result |= read_block (fd, fname, fdlen, shdr->sh_offset,
+				  shdr->sh_offset + shdr->sh_size);
+	}
     }
   while ((scn = elf_nextscn (elf, scn)) != NULL);
 
-- 
2.1.0

[PATCH] strings: Produce error when section data falls outside file.

[Mark Wielaard]

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https://bugzilla.redhat.com/show_bug.cgi?id=1170810

Reported-by: Alexander Cherepanov <cherepan@mccme.ru>
Signed-off-by: Mark Wielaard <mjw@redhat.com>
---
 src/ChangeLog |  5 +++++
 src/strings.c | 17 +++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/ChangeLog b/src/ChangeLog
index 904b3c9..66d6270 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,10 @@
 2014-12-26  Mark Wielaard  <mjw@redhat.com>
 
+	* strings.c (read_elf): Produce error when section data falls outside
+	file.
+
+2014-12-26  Mark Wielaard  <mjw@redhat.com>
+
 	* nm.c (show_symbols): Guard against divide by zero in error check.
 	Add section index number in error message.
 
diff --git a/src/strings.c b/src/strings.c
index f60e4b4..d1eb7b2 100644
--- a/src/strings.c
+++ b/src/strings.c
@@ -725,8 +725,21 @@ read_elf (Elf *elf, int fd, const char *fname, off64_t fdlen)
 	 actually have content.  */
       if (shdr != NULL && shdr->sh_type != SHT_NOBITS
 	  && (shdr->sh_flags & SHF_ALLOC) != 0)
-	result |= read_block (fd, fname, fdlen, shdr->sh_offset,
-			      shdr->sh_offset + shdr->sh_size);
+	{
+	  if (shdr->sh_offset > fdlen
+	      || fdlen - shdr->sh_offset < shdr->sh_size)
+	    {
+	      size_t strndx = 0;
+	      elf_getshdrstrndx (elf, &strndx);
+	      error (0, 0,
+		     gettext ("Skipping section %zd '%s' data outside file"),
+		     elf_ndxscn (scn), elf_strptr (elf, strndx, shdr->sh_name));
+	      result = 1;
+	    }
+	  else
+	    result |= read_block (fd, fname, fdlen, shdr->sh_offset,
+				  shdr->sh_offset + shdr->sh_size);
+	}
     }
   while ((scn = elf_nextscn (elf, scn)) != NULL);
 
-- 
2.1.0