Seq Segment Fault.

[Ryan Whited]

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.

[Eric Blake]

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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
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Re: Seq Segment Fault.

[Philip Rowlands]

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