strlim: avoid one-byte stack overflow

[aitap]

Since the limit is up to 500 characters, make sure to allocate 501 bytes, including the terminator at the end, avoiding the stack overflow introduced in #7005:

data.table::fread(text = paste0(
 strrep("mary had a little lamb\n", 100),
 strrep("a", 500), "\n", "a")
)

==5358==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffd0f20c7e4 at pc 0x7f06826bb311 bp 0x7ffd0f20ad90 sp 0x7ffd0f20ad88
WRITE of size 1 at 0x7ffd0f20c7e4 thread T0
    #0 0x7f06826bb310 in strlim /tmp/RtmpvbbbcM/R.INSTALLd607e4c6707/data.table/src/fread.c:235
    #1 0x7f06826bb310 in freadMain /tmp/RtmpvbbbcM/R.INSTALLd607e4c6707/data.table/src/fread.c:2947
    #2 0x7f06826c2d62 in freadR /tmp/RtmpvbbbcM/R.INSTALLd607e4c6707/data.table/src/freadR.c:229

Will this need a test? By itself the overflow is probably harmless, as it only writes a single zero into a place on the stack that doesn't seem to be used by anything, but it trips up sanitizers before other crashes can be reproduced, for example:

Details

options(warn=-1)
repeat
 sample(setdiff(1:32, 26), 1024, replace = TRUE) |>
 as.raw() |>
 rawToChar() |>
 data.table::fread(text = _) |>
 try()

...eventually:

free(): invalid next size (fast)

Program received signal SIGABRT, Aborted.

WRITE of size 4 at 0x6020001de644 thread T0                                                                                                                                        #0 0x7fae27ea04f2 in Field /tmp/Rtmpd8OIyO/R.INSTALL20227793d77d/data.table/src/fread.c:592                                                                                
    #1 0x7fae27eb4711 in freadMain /tmp/Rtmpd8OIyO/R.INSTALL20227793d77d/data.table/src/fread.c:2309
    #2 0x7fae27ec2d42 in freadR /tmp/Rtmpd8OIyO/R.INSTALL20227793d77d/data.table/src/freadR.c:229                                                                              

0x6020001de644 is located 4 bytes to the right of 16-byte region [0x6020001de630,0x6020001de640)    
allocated by thread T0 here:                                                                                                                                                   
    #0 0x7fae332b83b7 in __interceptor_calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:77                                                                       
    #1 0x7fae27eb445e in freadMain /tmp/Rtmpd8OIyO/R.INSTALL20227793d77d/data.table/src/fread.c:2295                                                                           
    #2 0x7fae27ec2d42 in freadR /tmp/Rtmpd8OIyO/R.INSTALL20227793d77d/data.table/src/freadR.c:229                                                                              

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.13%. Comparing base (2c17a5a) to head (86dbab2).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7408   +/-   ##
=======================================
  Coverage   99.13%   99.13%           
=======================================
  Files          85       85           
  Lines       16621    16621           
=======================================
  Hits        16477    16477           
  Misses        144      144           

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[github-actions]

• HEAD=strlim-overflow stopped early for fread(colClasses='Date') improved in #6107
• HEAD=strlim-overflow stopped early for fread(select=list(Date='date')) improved in #6107
• HEAD=strlim-overflow stopped early for DT[by,verbose=TRUE] improved in #6296
• HEAD=strlim-overflow stopped early for fread(colClasses=list(Date='date')) improved in #6107
  

Generated via commit 86dbab2

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	5 minutes and 15 seconds
Installing different package versions	10 minutes and 11 seconds
Running and plotting the test cases	2 minutes and 37 seconds

[MichaelChirico]

Would the simple example you shared be useful in the test suite?

data.table::fread(text = paste0(
 strrep("mary had a little lamb\n", 100),
 strrep("a", 500), "\n", "a")
)

[ben-schwen]

Would the simple example you shared be useful in the test suite?

data.table::fread(text = paste0(
 strrep("mary had a little lamb\n", 100),
 strrep("a", 500), "\n", "a")
)

I guess not since the error only surfaces with ASAN IINM

[aitap]

We have AddressSanitizer in GitLab CI. I don't mind adding a test if it is warranted.

[MichaelChirico]

LGTM!