linux-kernel - Wrong length / buffer overlow by the syslog syscall

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Message-ID: <CAF6-1L7qDULSvzaB2G=8y9Jkyd=SfcDBnNTxTuN0xSQxG94CHg@mail.gmail.com>
Date:	Wed, 5 Dec 2012 11:27:48 +0100
From:	Sylvain Munaut <s.munaut@...tever-company.com>
To:	linux-kernel@...r.kernel.org
Cc:	Jeff Mahoney <jeffm@...e.com>
Subject: Wrong length / buffer overlow by the syslog syscall

Hi,

I was debugging a segfault in the 'dmesg' utility that I finally
traced to the syslog syscall overflowing the buffer.
I'm under a 3.6.8 kernel and it has commit
e3756477aec028427fec767957c0d4b6cfb87208 present which apparently
fixed a similar issue, but I still have some occurence.

strace dmesg -s 8192

shows:

syslog(0x3, 0xb4e060, 0x2008)           = 8259

so despite being given a buffer of 8200 bytes, it writes 8259 ...

It happens on several machines and this only seem to happen if there
was a wrap around in the log buffer (it's a first observation on a
limited number of sample so it might be a coincidence)


Cheers,

    Sylvain

PS: Please cc me in any response, I'm not on the list.
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