| Message ID | 20221004062333.416225-1-usama.anjum@collabora.com |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] cifs: remove initialization value | expand |
Hi Usama, On 10/04, Muhammad Usama Anjum wrote: >Don't initialize the rc as its value is being overwritten before its >use. Being bitten by an unitialized variable bug as recent as 2 days ago, I'd say this is a step backwards from the "best practices" POV. >Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com> >--- > fs/cifs/smb2pdu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > >diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c >index 0600f0a07628..2bf43c892ae6 100644 >--- a/fs/cifs/smb2pdu.c >+++ b/fs/cifs/smb2pdu.c >@@ -879,7 +879,7 @@ SMB2_negotiate(const unsigned int xid, > struct smb2_negotiate_rsp *rsp; > struct kvec iov[1]; > struct kvec rsp_iov; >- int rc = 0; >+ int rc; > int resp_buftype; > int blob_offset, blob_length; > char *security_blob; >-- >2.30.2 Cheers, Enzo
Muhammad Usama Anjum <usama.anjum@collabora.com> writes: > Don't initialize the rc as its value is being overwritten before its > use. > > Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com> > --- > fs/cifs/smb2pdu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
merged into cifs-2.6.git for-next On Tue, Oct 4, 2022 at 2:09 PM Paulo Alcantara <pc@cjr.nz> wrote: > > Muhammad Usama Anjum <usama.anjum@collabora.com> writes: > > > Don't initialize the rc as its value is being overwritten before its > > use. > > > > Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com> > > --- > > fs/cifs/smb2pdu.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
From: Enzo Matsumiya > Sent: 04 October 2022 15:23 > > Hi Usama, > > On 10/04, Muhammad Usama Anjum wrote: > >Don't initialize the rc as its value is being overwritten before its > >use. > > Being bitten by an unitialized variable bug as recent as 2 days ago, I'd > say this is a step backwards from the "best practices" POV. Depends on your POV. If you don't initialise locals there is a fair chance that the compiler will detect buggy code. If you initialise them you get well defined behaviour - but the compiler won't find bugs for you. Mostly the kernel is in the first camp. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
On Tue, Oct 04, 2022 at 11:23:06AM -0300, Enzo Matsumiya wrote: > Hi Usama, > > On 10/04, Muhammad Usama Anjum wrote: > > Don't initialize the rc as its value is being overwritten before its > > use. > > Being bitten by an unitialized variable bug as recent as 2 days ago, I'd > say this is a step backwards from the "best practices" POV. Zero is a random bogus value. How likely is it that zero is the correct value or a negative error code is correct? There are probably a four to one ratio of error paths to success paths in the kernel (100% made up statistic). But mostly success paths end in "return 0;". So when you see a "return rc;" there is probably less than one in ten chance that rc is potentially zero. So there is an over 90% chance that zero is the wrong initializer to use. Meanwhile what initializing things to bogus values does is it disables static analysis checking for uninitialized value bugs. So it hides bugs until the user hits them. Disabling static analysis can make sense for a very complicated function but it's not best practice in general. On the other hand uninitialized memory is a source of security bugs. There are two ways to prevent this: 1) Use static analysis. Currently the GCC uninitialized variable warning is disabled because it is kind of rubbish but there are other static analysis tools out there. 2) Use the GCC extension to automatically initialize stack data to zero. regards, dan carpenter
On 10/05, David Laight wrote: >From: Enzo Matsumiya >> Sent: 04 October 2022 15:23 >> >> Hi Usama, >> >> On 10/04, Muhammad Usama Anjum wrote: >> >Don't initialize the rc as its value is being overwritten before its >> >use. >> >> Being bitten by an unitialized variable bug as recent as 2 days ago, I'd >> say this is a step backwards from the "best practices" POV. > >Depends on your POV. My POV was, considering "unitialized variables" is a _whole_ class of security bugs, a patch to specifically deinitialize a variable is pretty much like saying "let's leave this to chance". https://cwe.mitre.org/data/definitions/457.html >If you don't initialise locals there is a fair chance that the >compiler will detect buggy code. > >If you initialise them you get well defined behaviour - but >the compiler won't find bugs for you. > >Mostly the kernel is in the first camp. My money is on the smaller unfair chances that the compiler cannot catch even the smallest bit of complexity of uninitialized use. Also, initializing something to 0/NULL will, most of the time, if at all, be "just" a bug, whereas an uninitialized variable bug might turn into a security bug and even go unnoticed for years. Anyway, this patch got merged and I seem to be alone with this concern... > David Cheers, Enzo
diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c index 0600f0a07628..2bf43c892ae6 100644 --- a/fs/cifs/smb2pdu.c +++ b/fs/cifs/smb2pdu.c @@ -879,7 +879,7 @@ SMB2_negotiate(const unsigned int xid, struct smb2_negotiate_rsp *rsp; struct kvec iov[1]; struct kvec rsp_iov; - int rc = 0; + int rc; int resp_buftype; int blob_offset, blob_length; char *security_blob;
Don't initialize the rc as its value is being overwritten before its use. Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com> --- fs/cifs/smb2pdu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)