Messages in this thread | | | Subject | Re: [PATCH] nfc: st-nci: Fix an incorrect skb_buff size in 'st_nci_i2c_read()' | From | Christophe JAILLET <> | Date | Tue, 20 Aug 2019 07:33:39 +0200 |
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Le 12/08/2019 à 05:57, David Miller a écrit : > From: Christophe JAILLET <christophe.jaillet@wanadoo.fr> > Date: Tue, 6 Aug 2019 16:16:40 +0200 > >> In 'st_nci_i2c_read()', we allocate a sk_buff with a size of >> ST_NCI_I2C_MIN_SIZE + len. >> >> However, later on, we first 'skb_reserve()' ST_NCI_I2C_MIN_SIZE bytes, then >> we 'skb_put()' ST_NCI_I2C_MIN_SIZE bytes. >> Finally, if 'len' is not 0, we 'skb_put()' 'len' bytes. >> >> So we use ST_NCI_I2C_MIN_SIZE*2 + len bytes. >> >> This is incorrect and should already panic. I guess that it does not occur >> because of extra memory allocated because of some rounding. >> >> Fix it and allocate enough room for the 'skb_reserve()' and the 'skb_put()' >> calls. >> >> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> >> --- >> This patch is LIKELY INCORRECT. So think twice to what is the correct >> solution before applying it. >> Maybe the skb_reserve should be axed or some other sizes are incorrect. >> There seems to be an issue, that's all I can say. > The skb_reserve() should be removed,
I don't fully understand the potential implications, but looks ok to me. At least, the allocated memory and the size of the used memory would match.
What I don't understand is why is does not BUG_ON with the current code. Does my suspected "over allocation" because of rounding/aligment could hide the issue?
A Tested-by: by someone who has the corresponding hardware would also be useful IMHO.
> and the second memcpy() should remove > the " + ST_NCI_I2C_MIN_SIZE". Hmm, not sure on this one.
The skb is manipulated only with skb_put. So only the tail pointer and len are updated. The data pointer remains at the same position, so there should effectively be an offset of ST_NCI_I2C_MIN_SIZE for the 2nd memcpy.
Maybe, using skb_put_data would be cleaner here, in order to "concatenate" these 2 parts without having to handle by hand the right position in the buffer.
If you agree, I'll send a V2.
Thx for the review and comments.
CJ
> This SKB just get sent down to ndlc_recv() so the content returned from I2C > should places at skb->data to be processed. > > Pretty clear this code was never tested.
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