Seq Segment Fault.
Here is my code.
#!/bin/bash
echo "Add directions here."
read URL
read NUM1
read NUM2
read EXT
echo "Please choose a folder name."
read NAM
mkdir $HOME/$NAM
cd $HOME/$NAM
for i in $(seq -w $NUM1 $NUM2); do wget "$URL${i}$EXT"; done
I was testing out my script, and I came across an instance where I had
a large "i" (it started at 00 and went to 99). It
processed for a few minutes (my poor intel atom) and returned with a
"Segmentation fault". From what I know from Assembly, I think this is
a buffer overflow which could allow for malicious code injection.
Please let me know if I can be of further assistance.
--
Peace Out and Rock On,
Ryan Whited
Re: Seq Segment Fault.
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 According to Ryan Whited on 9/18/2009 4:38 AM: > #!/bin/bash > for i in $(seq -w $NUM1 $NUM2) Are you sure your segfault is in seq, or is it in bash? You neglected to mention which versions you were using: bash --version seq --version However, it seems to me that your problem is that bash tries to slurp all of $() into memory, and seq generated so much data that bash ran out of memory (or overflowed its stack). In other words, it is not a segfault in seq, but bash that crashed, and because you exceeded the limits of what your machine will support. - -- Don't work too hard, make some time for fun as well! Eric Blake e...@byu.net -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.9 (Cygwin) Comment: Public key at home.comcast.net/~ericblake/eblake.gpg Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkqzde8ACgkQ84KuGfSFAYAbHgCgnNr01KRBNuhsC2ifQOEcgx4f okQAn2i/cc4inQM46UOq5WeMAsxJnwpj =s0aj -END PGP SIGNATURE-
Re: Seq Segment Fault.
On Fri, 18 Sep 2009, Eric Blake wrote:
However, it seems to me that your problem is that bash tries to slurp all
of $() into memory, and seq generated so much data that bash ran out of
memory (or overflowed its stack).
It's certainly possible for bash to run out of stack and crash with
SIGSEGV.
$ bash -c 'recurse() { recurse; }; recurse'
Segmentation fault
for i in $(seq -w $NUM1 $NUM2); do wget "$URL${i}$EXT"; done
This could be rewritten as
seq -w $NUM1 $NUM2 | while read i ; do wget "$URL${i}$EXT"; done
to prevent all of seq's output having to be buffered at once.
Cheers,
Phil
Re: Seq Segment Fault.
Bash version 3.2.48(1)-release (i486-pc-linux-gnu) Seq (GNU coreutils) 6.10 I apologize for my lack information. I could be bash, in fact that was my first theory, but I decided to watch top while I let it run, and Terminal never went over 2% memory usage. Although it's possible I'm looking in the wrong spot. Bug reports isn't something I do everyday. Also, thank you for that bit of code. I'll try it and see if it helps anything. Again, if I can be of any further assistance. Let me know. On Fri, Sep 18, 2009 at 7:58 AM, Eric Blake wrote: > -BEGIN PGP SIGNED MESSAGE- > Hash: SHA1 > > According to Ryan Whited on 9/18/2009 4:38 AM: >> #!/bin/bash >> for i in $(seq -w $NUM1 $NUM2) > > Are you sure your segfault is in seq, or is it in bash? You neglected to > mention which versions you were using: > > bash --version > seq --version > > However, it seems to me that your problem is that bash tries to slurp all > of $() into memory, and seq generated so much data that bash ran out of > memory (or overflowed its stack). In other words, it is not a segfault in > seq, but bash that crashed, and because you exceeded the limits of what > your machine will support. > > - -- > Don't work too hard, make some time for fun as well! > > Eric Blake e...@byu.net > -BEGIN PGP SIGNATURE- > Version: GnuPG v1.4.9 (Cygwin) > Comment: Public key at home.comcast.net/~ericblake/eblake.gpg > Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ > > iEYEARECAAYFAkqzde8ACgkQ84KuGfSFAYAbHgCgnNr01KRBNuhsC2ifQOEcgx4f > okQAn2i/cc4inQM46UOq5WeMAsxJnwpj > =s0aj > -END PGP SIGNATURE- > -- Peace Out and Rock On, Ryan Whited
